Table of Contents

Class ResultLinqExtensions

Namespace
FunctionalDdd
Assembly
FunctionalDdd.RailwayOrientedProgramming.dll

Provides LINQ query expression support for Result types, enabling C# query syntax for functional operations.

public static class ResultLinqExtensions
Inheritance
ResultLinqExtensions
Inherited Members

Examples

// Using LINQ query syntax with Result
var result = from firstName in FirstName.TryCreate(firstNameInput)
             from lastName in LastName.TryCreate(lastNameInput)
             from email in EmailAddress.TryCreate(emailInput)
             where email.Value.EndsWith("@company.com")
             select new User(firstName, lastName, email);

// This is equivalent to:
var result2 = FirstName.TryCreate(firstNameInput)
    .Bind(firstName => LastName.TryCreate(lastNameInput)
        .Bind(lastName => EmailAddress.TryCreate(emailInput)
            .Ensure(email => email.Value.EndsWith("@company.com"), 
                    Error.Validation("Must be company email"))
            .Map(email => new User(firstName, lastName, email))));

Remarks

These extension methods allow you to use LINQ query syntax (from, select, where) with Result types, making functional composition more readable and familiar to C# developers.

The mapping is: - Select maps to Map<TIn, TOut>(Result<TIn>, Func<TIn, TOut>) - SelectMany maps to Bind<TValue, TResult>(Result<TValue>, Func<TValue, Result<TResult>>) - Where maps to Ensure<TValue>(Result<TValue>, Func<TValue, bool>, Error)

Methods

SelectMany<TSource, TCollection, TResult>(Result<TSource>, Func<TSource, Result<TCollection>>, Func<TSource, TCollection, TResult>)

Projects each value of a Result to a new Result and flattens the result (LINQ SelectMany operation). Enables composition of multiple Result-returning operations in LINQ query syntax.

public static Result<TResult> SelectMany<TSource, TCollection, TResult>(this Result<TSource> source, Func<TSource, Result<TCollection>> collectionSelector, Func<TSource, TCollection, TResult> resultSelector)

Parameters

source Result<TSource>

The source result.

collectionSelector Func<TSource, Result<TCollection>>

A function that returns a Result based on the source value.

resultSelector Func<TSource, TCollection, TResult>

A function to create the final result from the source and collection values.

Returns

Result<TResult>

A new Result with the final projected value, or the first failure encountered.

Type Parameters

TSource

The type of the source value.

TCollection

The type of the intermediate collection value.

TResult

The type of the final result value.

Remarks

This is the key method that enables LINQ query syntax with multiple 'from' clauses. It performs monadic bind followed by a projection.

Select<TIn, TOut>(Result<TIn>, Func<TIn, TOut>)

Projects the value of a successful Result using a selector function (LINQ Select operation). Maps to Map<TIn, TOut>(Result<TIn>, Func<TIn, TOut>).

public static Result<TOut> Select<TIn, TOut>(this Result<TIn> result, Func<TIn, TOut> selector)

Parameters

result Result<TIn>

The result to project.

selector Func<TIn, TOut>

The projection function to apply to the value.

Returns

Result<TOut>

A new Result with the projected value, or the original failure.

Type Parameters

TIn

The type of the input value.

TOut

The type of the output value.

Where<TSource>(Result<TSource>, Func<TSource, bool>)

Filters a Result based on a predicate (LINQ Where operation). If the predicate returns false, converts the success Result to a failure.

public static Result<TSource> Where<TSource>(this Result<TSource> source, Func<TSource, bool> predicate)

Parameters

source Result<TSource>

The result to filter.

predicate Func<TSource, bool>

The predicate to test the value against.

Returns

Result<TSource>

The original success Result if the predicate is true; otherwise a failure Result with a generic error.

Type Parameters

TSource

The type of the source value.

Examples

// Using Where in query syntax (generic error)
var result = from user in GetUser(id)
             where user.IsActive
             select user;

// Better: Use Ensure for custom error
var betterResult = GetUser(id)
    .Ensure(u => u.IsActive, Error.Domain("User is not active"));

Remarks

This method returns a generic "filtered out" error message. For more meaningful error messages, use Ensure<TValue>(Result<TValue>, Func<TValue, bool>, Error) directly instead.

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