Method DoWhile

DoWhile<TSource>(IEnumerable<TSource>, Func<bool>)

Generates an enumerable sequence by repeating a source sequence as long as the given loop postcondition holds.

Declaration

public static IEnumerable<TSource> DoWhile<TSource>(this IEnumerable<TSource> source, Func<bool> condition)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	Source sequence to repeat while the condition evaluates true.
Func<bool>	condition	Loop condition.

Returns

Type	Description
IEnumerable<TSource>	Sequence generated by repeating the given sequence until the condition evaluates to false.

Type Parameters

Name	Description
TSource	Source sequence element type.

Remarks

condition is evaluated lazily, once at the end of each loop of source.

source is cached via Memoize<TSource>(IEnumerable<TSource>, bool), so that it is only iterated once during the first loop. Successive loops will enumerate the cache instead of source.

Examples

The following code example demonstrates how to repeat a sequence as long as a condition is true, using DoWhile.

var executionCount = 0;
var sequence = Enumerable.Range(1, 5)
    .Do(_ => executionCount++);
            
// Execute an action for each element
var loopCount = 0;
var result = sequence
    .DoWhile(() => loopCount++ < 2);

Console.WriteLine($"Before (execCount: {executionCount})");

Console.WriteLine(
    "[" +
    string.Join(", ", result) +
    "]");

Console.WriteLine($"After (execCount: {executionCount})");

// This code produces the following output:
// Before (execCount: 0)
// [1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5]
// After (execCount: 5)

Exceptions

Type	Condition
ArgumentNullException	source or condition is null.