Struct Result<T>

Namespace: Rascal

Assembly: Rascal.dll

A type which contains either an ok value or an error.

public readonly struct Result<T> : IEquatable<T>, IEquatable<Result<T>>

Type Parameters

T: The type of an ok value.

Implements: IEquatable<T>

IEquatable<Result<T>>

Inherited Members: object.Equals(object, object)

object.GetType()

object.ReferenceEquals(object, object)

Constructors

Result(Error)

Creates a new result with an error.

public Result(Error error)

Parameters

error Error: The error of the result.

Result(T)

Creates a new result with an ok value.

public Result(T value)

Parameters

value T: The ok value.

Properties

IsError

Whether the result is an error.

public bool IsError { get; }

Property Value

bool: A type which contains either an ok value or an error.

Remarks

This is always the inverse of IsOk but is more specific about intent.

IsOk

Whether the result is ok.

public bool IsOk { get; }

Property Value

bool: A type which contains either an ok value or an error.

Methods

AsRef()

Gets an immutable reference to the ok value of the result.

[Pure]
public ref readonly T? AsRef()

Returns

T: An immutable reference to the ok value. The value of the reference might be default if the result is an error.

Combine<TOther>(Result<TOther>)

Combines the result with another result.

[Pure]
public Result<(T first, TOther second)> Combine<TOther>(Result<TOther> other)

Parameters

other Result<TOther>: The result to combine the current result with.

Returns

Result<(T first, TOther second)>: A result containing a tuple of the ok value of the current result and the ok value of other. If either of the results are errors, returns a result containing that error, or both errors if both results are errors.

Type Parameters

TOther: The type of the ok value in the other result.

Const<TNew>(TNew)

Replaces the ok value of the result with a new value, or does nothing if the result is an error.

[Pure]
public Result<TNew> Const<TNew>(TNew newValue)

Parameters

newValue TNew: The new value to replace the ok value of the result with.

Returns

Result<TNew>: A result which is either newValue if the original result was ok, or an error if the original result was an error.

Type Parameters

TNew: The type of the new value.

Equals(Result<T>)

Checks whether the result is equal to another result. Results are equal if both results are ok and the ok values are equal, or if both results are errors.

[Pure]
public bool Equals(Result<T> other)

Parameters

other Result<T>: The result to check for equality with the current result.

Returns

bool: A type which contains either an ok value or an error.

Equals(Result<T>, IEqualityComparer<T>)

Checks whether the result is equal to another result using a specified equality comparer. Results are equal if both results are ok and the ok values are equal, or if both results are errors.

[Pure]
public bool Equals(Result<T> other, IEqualityComparer<T> valueComparer)

Parameters

other Result<T>: The result to check for equality with the current result.
valueComparer IEqualityComparer<T>: The equality comparer to use for comparing values.

Returns

bool: A type which contains either an ok value or an error.

Equals(object?)

[Pure]
public override bool Equals(object? other)

Parameters

other object: A type which contains either an ok value or an error.

Returns

bool: A type which contains either an ok value or an error.

Equals(T?)

Checks whether the result is ok and the ok value is equal to another value.

[Pure]
public bool Equals(T? other)

Parameters

other T: The value to check for equality with the ok value of the result.

Returns

bool: A type which contains either an ok value or an error.

Equals(T?, IEqualityComparer<T>)

Checks whether the result is ok and the ok value is equal to another value using a specified equality comparer.

[Pure]
public bool Equals(T? other, IEqualityComparer<T> valueComparer)

Parameters

other T: The value to check for equality with the ok value of the result.
valueComparer IEqualityComparer<T>: The equality comparer to use for comparing values.

Returns

bool: A type which contains either an ok value or an error.

Expect(string)

Expects the result to be ok, throwing an UnwrapException with a specified message if the result is an error.

[Pure]
public T Expect(string error)

Parameters

error string: The message to construct the UnwrapException to throw using if the result is an error.

Returns

T: The ok value of the result.

Remarks

This API is unsafe in the sense that it might intentionally throw an exception. Please only use this API if the caller knows without a reasonable shadow of a doubt that this operation is safe, or that an exception is acceptable to be thrown.

Exceptions

UnwrapException: The result is an error.

GetHashCode()

[Pure]
public override int GetHashCode()

Returns

int: A type which contains either an ok value or an error.

GetValueOr(Func<Error, T>)

Gets the ok value of the result, or a default value if the result is an error.

[Pure]
public T GetValueOr(Func<Error, T> getValue)

Parameters

getValue Func<Error, T>: A function to get a value to return if the result is an error.

Returns

T

GetValueOr(Func<T>)

Gets the ok value of the result, or a default value if the result is an error.

[Pure]
public T GetValueOr(Func<T> getDefault)

Parameters

getDefault Func<T>: A function to get a default value to return if the result is an error.

Returns

T: A type which contains either an ok value or an error.

GetValueOr(T)

Gets the ok value of the result, or a default value if the result is an error.

[Pure]
public T GetValueOr(T @default)

Parameters

default T: The default value to return if the result is an error.

Returns

T: A type which contains either an ok value or an error.

GetValueOrDefault()

Gets the ok value of the result, or default if the result is an error.

[Pure]
public T? GetValueOrDefault()

Returns

T: A type which contains either an ok value or an error.

MapAsync<TNew>(Func<T, Task<TNew>>)

Maps the ok value of the result using an asynchronous mapping function, or does nothing if the result is an error.

[Pure]
public Task<Result<TNew>> MapAsync<TNew>(Func<T, Task<TNew>> mapping)

Parameters

mapping Func<T, Task<TNew>>: The function used to map the ok value.

Returns

Task<Result<TNew>>: A new result containing either the mapped ok value or the error of the original result.

Type Parameters

TNew: The type of the new value.

MapError(Func<Error, Error>)

Maps the error in the result if it is an error and returns a new result containing the mapped error. Otherwise, returns the current result.

[Pure]
public Result<T> MapError(Func<Error, Error> mapping)

Parameters

mapping Func<Error, Error>: The function used to map the error.

Returns

Result<T>: A result which contains either the mapped error or the ok value of the original result.

Map<TNew>(Func<T, TNew>)

Maps the ok value of the result using a mapping function, or does nothing if the result is an error.

[Pure]
public Result<TNew> Map<TNew>(Func<T, TNew> mapping)

Parameters

mapping Func<T, TNew>: The function used to map the ok value.

Returns

Result<TNew>: A new result containing either the mapped ok value or the error of the original result.

Type Parameters

TNew: The type of the new value.

MatchAsync<TResult>(Func<T, Task<TResult>>, Func<Error, Task<TResult>>)

Asynchronously matches over the ok value or error of the result and returns another value. Can be conceptualized as an exhaustive switch expression matching all possible values of the type.

[Pure]
public Task<TResult> MatchAsync<TResult>(Func<T, Task<TResult>> ifOk, Func<Error, Task<TResult>> ifError)

Parameters

ifOk Func<T, Task<TResult>>: The function to apply to the ok value of the result if the result is ok.
ifError Func<Error, Task<TResult>>: The function to apply to the result's error if the result is an error.

Returns

Task<TResult>: The result of applying either ifOk or ifError on the ok value or error of the result.

Type Parameters

TResult: The type to return from the match.

Match<TResult>(Func<T, TResult>, Func<Error, TResult>)

Matches over the ok value or error of the result and returns another value. Can be conceptualized as an exhaustive switch expression matching all possible values of the type.

[Pure]
public TResult Match<TResult>(Func<T, TResult> ifOk, Func<Error, TResult> ifError)

Parameters

ifOk Func<T, TResult>: The function to apply to the ok value of the result if the result is ok.
ifError Func<Error, TResult>: The function to apply to the result's error if the result is an error.

Returns

TResult: The result of applying either ifOk or ifError on the ok value or error of the result.

Type Parameters

TResult: The type to return from the match.

SelectMany<TNew>(Func<T, Result<TNew>>)

Maps the ok value of the result to a new result using a mapping function, or does nothing if the result is an error.

[Pure]
public Result<TNew> SelectMany<TNew>(Func<T, Result<TNew>> mapping)

Parameters

mapping Func<T, Result<TNew>>: The function used to map the ok value to a new result.

Returns

Result<TNew>: A result which is either the mapped result or a new result containing the error of the original result.

Type Parameters

TNew: The type of the new value.

SelectMany<TOther, TNew>(Func<T, Result<TOther>>, Func<T, TOther, TNew>)

Maps the ok value of the result to an intermediate result using a mapping function, then applies another mapping function onto the ok values of the original and intermediate results, or does nothing if either of the results is an error.

[Pure]
public Result<TNew> SelectMany<TOther, TNew>(Func<T, Result<TOther>> other, Func<T, TOther, TNew> mapping)

Parameters

other Func<T, Result<TOther>>: The function used to map the ok value to an intermediate result.
mapping Func<T, TOther, TNew>: The function used to map the ok value and ok value of the intermediate result to a new result.

Returns

Result<TNew>: A result constructed by applying mapping onto the ok value contained in the result returned by other as well as the ok value in the original result, or a new result containing the error of the original or intermediate results.

Type Parameters

TOther: The type of the intermediate value.
TNew: The type of the new value.

Remarks

The expression r.SelectMany(x => f(x), (x, y) => g(x, y)) can be written as r.Bind(x => f(x).Map(y => g(x, y))).

Select<TNew>(Func<T, TNew>)

Maps the ok value of the result using a mapping function, or does nothing if the result is an error.

[Pure]
public Result<TNew> Select<TNew>(Func<T, TNew> mapping)

Parameters

mapping Func<T, TNew>: The function used to map the ok value.

Returns

Result<TNew>: A new result containing either the mapped ok value or the error of the original result.

Type Parameters

TNew: The type of the new value.

Switch(Action<T>, Action<Error>)

Matches over the ok value or error of the result and invokes an effect-ful action onto the ok value or error. Can be conceptualized as an exhaustive switch statement matching all possible values of the type.

public void Switch(Action<T> ifOk, Action<Error> ifError)

Parameters

ifOk Action<T>: The function to call with the ok value of the result if the result is ok.
ifError Action<Error>: The function to call with the result's error if the result is an error.

SwitchAsync(Func<T, Task>, Func<Error, Task>)

Asynchronously matches over the ok value or error of the result and invokes an effect-ful action onto the ok value or error. Can be conceptualized as an exhaustive switch statement matching all possible values of the type.

public Task SwitchAsync(Func<T, Task> ifOk, Func<Error, Task> ifError)

Parameters

ifOk Func<T, Task>: The function to call with the ok value of the result if the result is ok.
ifError Func<Error, Task>: The function to call with the result's error if the result is an error.

Returns

Task: A type which contains either an ok value or an error.

ThenAsync<TNew>(Func<T, Task<Result<TNew>>>)

Maps the ok value of the result to a new result using an asynchronous mapping function, or does nothing if the result is an error.

[Pure]
public Task<Result<TNew>> ThenAsync<TNew>(Func<T, Task<Result<TNew>>> mapping)

Parameters

mapping Func<T, Task<Result<TNew>>>: The function used to map the ok value to a new result.

Returns

Task<Result<TNew>>: A result which is either the mapped result or a new result containing the error of the original result.

Type Parameters

TNew: The type of the new value.

ThenTryAsync<TNew>(Func<T, Task<Result<TNew>>>)

Tries to map the ok value of the result to a new result using an asynchronous mapping function, or does nothing if the result is an error. If the mapping function throws an exception, the exception will be returned wrapped in an ExceptionError.

[Pure]
public Task<Result<TNew>> ThenTryAsync<TNew>(Func<T, Task<Result<TNew>>> mapping)

Parameters

mapping Func<T, Task<Result<TNew>>>: The function used to map the ok value to a new result.

Returns

Task<Result<TNew>>: A result which is either the mapped result, the exception thrown by mapping wrapped in an ExceptionError, or a new result containing the error of the original result.

Type Parameters

TNew: The type of the new value.

ThenTry<TNew>(Func<T, Result<TNew>>)

Tries to map the ok value of the result to a new result using a mapping function, or does nothing if the result is an error. If the mapping function throws an exception, the exception will be returned wrapped in an ExceptionError.

[Pure]
public Result<TNew> ThenTry<TNew>(Func<T, Result<TNew>> mapping)

Parameters

mapping Func<T, Result<TNew>>: The function used to map the ok value to a new result.

Returns

Result<TNew>: A result which is either the mapped result, the exception thrown by mapping wrapped in an ExceptionError, or a new result containing the error of the original result.

Type Parameters

TNew: The type of the new value.

Then<TNew>(Func<T, Result<TNew>>)

Maps the ok value of the result to a new result using a mapping function, or does nothing if the result is an error.

[Pure]
public Result<TNew> Then<TNew>(Func<T, Result<TNew>> mapping)

Parameters

mapping Func<T, Result<TNew>>: The function used to map the ok value to a new result.

Returns

Result<TNew>: A result which is either the mapped result or a new result containing the error of the original result.

Type Parameters

TNew: The type of the new value.

ToEnumerable()

Creates a IEnumerable<T> from the result.

[Pure]
public IEnumerable<T> ToEnumerable()

Returns

IEnumerable<T>: A IEnumerable<T> containing either only the ok value of the result, or no values at all if the result is an error.

ToString()

Gets a string representation of the result.

[Pure]
public override string ToString()

Returns

string: A type which contains either an ok value or an error.

To<TOther>(Error?)

Tries to convert the ok value of the result to another type.

[Pure]
public Result<TOther> To<TOther>(Error? error = null)

Parameters

error Error: The error to return if the ok value cannot be converted to TOther.

Returns

Result<TOther>: A result which contains the ok value converted to TOther, error if the ok value cannot be converted to TOther, or the error of the result if it is an error.

Type Parameters

TOther: The type to which to try convert the ok value.

TryGetError(out Error)

Tries to get an error from the result.

[Pure]
public bool TryGetError(out Error error)

Parameters

error Error: The error of the result.

Returns

bool: Whether the result is an error.

TryGetError(out Error, out T)

Tries to get an error from the result.

[Pure]
public bool TryGetError(out Error error, out T value)

Parameters

error Error: The error of the result.
value T: The ok value of the result.

Returns

bool: Whether the result is an error.

TryGetValue(out T)

Tries to get the ok value from the result.

[Pure]
public bool TryGetValue(out T value)

Parameters

value T: The ok value of the result.

Returns

bool: Whether the result is ok.

TryGetValue(out T, out Error)

Tries to get the ok value from the result.

[Pure]
public bool TryGetValue(out T value, out Error error)

Parameters

value T: The ok value of the result.
error Error: The error of the result.

Returns

bool: Whether the result is ok.

TryMapAsync<TNew>(Func<T, Task<TNew>>)

Tries to map the ok value of the result using an asynchronous mapping function, or does nothing if the result is an error. If the mapping function throws an exception, the exception will be returned wrapped in an ExceptionError.

[Pure]
public Task<Result<TNew>> TryMapAsync<TNew>(Func<T, Task<TNew>> mapping)

Parameters

mapping Func<T, Task<TNew>>: The function used to map the ok value.

Returns

Task<Result<TNew>>: A new result containing either the mapped ok value, the exception thrown by mapping wrapped in an ExceptionError, or the error of the original result.

Type Parameters

TNew: The type of the new value.

TryMap<TNew>(Func<T, TNew>)

Tries to map the ok value of the result using a mapping function, or does nothing if the result is an error. If the mapping function throws an exception, the exception will be returned wrapped in an ExceptionError.

[Pure]
public Result<TNew> TryMap<TNew>(Func<T, TNew> mapping)

Parameters

mapping Func<T, TNew>: The function used to map the ok value.

Returns

Result<TNew>: A new result containing either the mapped value, the exception thrown by mapping wrapped in an ExceptionError, or the error of the original result.

Type Parameters

TNew: The type of the new value.

Unwrap()

Unwraps the ok value of the result. Throws an UnwrapException if the result is an error.

[Pure]
public T Unwrap()

Returns

T: The ok value of the result.

Remarks

Exceptions

UnwrapException: The result is not ok.

Validate(Func<T, bool>, Func<T, Error>?)

Checks whether the ok value in the result matches a predicate, and if not replaces the value with an error.

[Pure]
public Result<T> Validate(Func<T, bool> predicate, Func<T, Error>? getError = null)

Parameters

predicate Func<T, bool>: The predicate to match the ok value against.
getError Func<T, Error>: A function to produce an error if the ok value doesn't match the predicate.

Returns

Result<T>: A result which contains the ok value of the original result if said value matches predicate, otherwise an error produced by getError. If the original result is an error, that error will be returned.

Where(Func<T, bool>)

Checks whether the ok value of the result matches a predicate, and if not replaces the value with an error.

[Pure]
public Result<T> Where(Func<T, bool> predicate)

Parameters

predicate Func<T, bool>: The predicate to match the ok value against.

Returns

Result<T>: A result which contains the ok value of the original result if said value matches predicate, otherwise an error. If the original result is an error, that error will be returned.

Operators

operator ==(Result<T>, Result<T>)

Checks whether two results are equal. Results are equal if both results are ok and the ok values are equal, or if both results are errors.

[Pure]
public static bool operator ==(Result<T> a, Result<T> b)

Parameters

a Result<T>: The first result to compare.
b Result<T>: The second result to compare.

Returns

bool: A type which contains either an ok value or an error.

operator ==(Result<T>, T?)

Checks whether a result is ok and the ok value is equal to another value.

[Pure]
public static bool operator ==(Result<T> a, T? b)

Parameters

a Result<T>: The result to compare.
b T: The value to check for equality with the ok value in the result.

Returns

bool: A type which contains either an ok value or an error.

explicit operator T(Result<T>)

Unwraps the ok value of the result. Throws an UnwrapException if the result is an error.

[Pure]
public static explicit operator T(Result<T> result)

Parameters

result Result<T>: A type which contains either an ok value or an error.

Returns

T: The ok value of the result.

Remarks

Exceptions

UnwrapException: The result is not ok.

implicit operator Result<T>(Error)

Implicitly constructs a result from an error.

[Pure]
public static implicit operator Result<T>(Error error)

Parameters

error Error: The error to construct the result from.

Returns

Result<T>: A type which contains either an ok value or an error.

implicit operator Result<T>(T)

Implicitly constructs a result from an ok value.

[Pure]
public static implicit operator Result<T>(T value)

Parameters

value T: The value to construct the result from.

Returns

Result<T>: A type which contains either an ok value or an error.

operator !=(Result<T>, Result<T>)

Checks whether two results are not equal. Results are equal if both results are ok and the ok values are equal, or if both results are errors.

[Pure]
public static bool operator !=(Result<T> a, Result<T> b)

Parameters

a Result<T>: The first result to compare.
b Result<T>: The second result to compare.

Returns

bool: A type which contains either an ok value or an error.

operator !=(Result<T>, T?)

Checks whether a result either does not have a value, or the value is not equal to another value.

[Pure]
public static bool operator !=(Result<T> a, T? b)

Parameters

a Result<T>: The result to compare.
b T: The value to check for inequality with the ok value in the result.

Returns

bool: A type which contains either an ok value or an error.

Table of Contents

Struct Result<T>

Type Parameters

Constructors

Result(Error)

Parameters

Result(T)

Parameters

Properties

IsError

Property Value

Remarks

IsOk

Property Value

Methods

AsRef()

Returns

Combine<TOther>(Result<TOther>)

Parameters

Returns

Type Parameters

Const<TNew>(TNew)

Parameters

Returns

Type Parameters

Equals(Result<T>)

Parameters

Returns

Equals(Result<T>, IEqualityComparer<T>)

Parameters

Returns

Equals(object?)

Parameters

Returns

Equals(T?)

Parameters

Returns

Equals(T?, IEqualityComparer<T>)

Parameters

Returns

Expect(string)

Parameters

Returns

Remarks

Exceptions

GetHashCode()

Returns

GetValueOr(Func<Error, T>)

Parameters

Returns

GetValueOr(Func<T>)

Parameters

Returns

GetValueOr(T)

Parameters

Returns

GetValueOrDefault()

Returns

MapAsync<TNew>(Func<T, Task<TNew>>)

Parameters

Returns

Type Parameters

MapError(Func<Error, Error>)

Parameters

Returns

Map<TNew>(Func<T, TNew>)

Parameters

Returns

Type Parameters

MatchAsync<TResult>(Func<T, Task<TResult>>, Func<Error, Task<TResult>>)

Parameters

Returns

Type Parameters

Match<TResult>(Func<T, TResult>, Func<Error, TResult>)

Parameters

Returns

Type Parameters

SelectMany<TNew>(Func<T, Result<TNew>>)

Parameters

Returns