Merge pull request #3 from RougeWare/feature/echo

Added `echo` functions

Author: KyNorthstar

README.md

@@ -45,6 +45,21 @@ let add = curry(+)
 ```
 
 
+## `echo` ##
+
+Simply returns what it's given. This is useful for reusing the input of higher-order functions.
+For example:
+```swift
+let withoutNils = arrayOfOptionals.compactMap(echo)
+```
+
+It's also useful for flattening collections of generators.
+For example:
+```swift
+let values = generators.map(echo)
+```
+
+
 ## Function Types ##
 
 Some typealiases for common functions:

Sources/FunctionTools/Echo.swift

@@ -0,0 +1,37 @@
+//
+//  Echo.swift
+//  FunctionTools
+//
+//  Created by Ben Leggiero on 2020-05-20.
+//  Copyright © 2020 Ben Leggiero BS-1-PS.
+//
+
+import Foundation
+
+
+
+/// A utility function which simply returns the given value.
+/// This is useful for reusing the input of higher-order functions.
+///
+/// For example:
+/// ```swift
+/// let withoutNils = arrayOfOptionals.compactMap(echo)
+/// ```
+///
+/// - Parameter input: The value to return
+@inlinable
+public func echo<T>(_ input: T) -> T { input }
+
+
+/// A utility function which simply returns the result of the given function.
+/// This is useful for flattening collections of generators.
+///
+/// For example:
+/// ```swift
+/// let values = generators.map(echo)
+/// ```
+///
+/// - Parameter inputGenerator: The function which generates a value
+/// - Throws: Anything `inputGenerator` throws
+@inlinable
+public func echo<T>(_ inputGenerator: ThrowingGenerator<T>) rethrows -> T { try inputGenerator() }