Tkheikkila.FunctionalTypes 2.0.0

Tkheikkila.FunctionalTypes

Useful types missing from C#

Inspired by Rust's std::unit, std::option::Option, and std::result::Result.

Unit

AKA: void

Contains no information other that it's type.

Maybe<T>

AKA: Option or Optional

A value that may or may not contain a value of type T.

This type has two states:

• Some that contains a single value of type T
  Created by calling Maybe<T>.Some(value).
• None that contains no value
  Created by calling Maybe<T>.None() or by returning default.

Result<TValue, TError>

AKA: Either

A value that can be in one of two states, but never both.

These states are:

• Ok that indicates success with a value of type TValue
  Created by calling Result<TValue, TError>.Ok(value).
• Error that indicates failure with a value of type TError
  Created by calling Result<TValue, TError>.Error(error)

MaybeResult<TValue, TError>

A combination of Maybe<T> and Result<TValue, TError>.

Equivalent to Maybe<Result<TValue, TError>>

Resembles Result<Maybe<TValue>, TError> and Result<TValue, Maybe<TError>>

This type has three states:

• Ok that indicates success with a value of type TValue Created by calling MaybeResult<TValue, TError>.Ok(value).
• Error that indicates failure with a value of type TError Created by calling MaybeResult<TValue, TError>.Error(error).
• Neither that indicates that neither a value of type TValue nor a value of type TError is present Created by calling MaybeResult<TValue, TError>.Neither().

GreedyValidationResult<TValue, TError>

A value that contains a value of type TValue and a collection of errors of type TError.

Resembles Result<TValue, List<TError>> with a value of type TValue that is always present.

Resembles LazyValidationResult<TValue, TError> with a collection of errors of type TError.

This type has two states:

• Valid that contains no errors
• Invalid that contains one or more errors of type TError

Created by calling Validation.Greedy<TValue, TError>(value).

Errors can be added by calling AddError(error), one of the AddErrors overloads, or one of the Validate overloads that returns a value of TError.

LazyValidationResult<TValue, TError>

A value that contains a value of type TValue. If the value is invalid, it also contains a single error of type TError.

Resembles GreedyValidationResult<TValue, TError> with a maximum of one error.

Resembles Result<TValue, TError> with a value of type TValue that is always present.

This type has two states:

• Valid that contains no errors
• Invalid that contains single error of type TError

Created by calling Validation.Lazy<TValue, TError>(value).

Error can be set by calling one of the Validate overloads that returns a value of TError.