// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information. using System; using System.Collections.Generic; using System.Linq; using System.Threading; namespace System.Linq { public static partial class EnumerableEx { /// <summary> /// Generates an enumerable sequence by repeating a source sequence as long as the given loop condition holds. /// </summary> /// <typeparam name="TResult">Result sequence element type.</typeparam> /// <param name="condition">Loop condition.</param> /// <param name="source">Sequence to repeat while the condition evaluates true.</param> /// <returns>Sequence generated by repeating the given sequence while the condition evaluates to true.</returns> public static IEnumerable<TResult> While<TResult>(Func<bool> condition, IEnumerable<TResult> source) { if (condition == null) throw new ArgumentNullException("condition"); if (source == null) throw new ArgumentNullException("source"); return WhileCore(condition, source).Concat(); } static IEnumerable<IEnumerable<TSource>> WhileCore<TSource>(Func<bool> condition, IEnumerable<TSource> source) { while (condition()) yield return source; } /// <summary> /// Returns an enumerable sequence based on the evaluation result of the given condition. /// </summary> /// <typeparam name="TResult">Result sequence element type.</typeparam> /// <param name="condition">Condition to evaluate.</param> /// <param name="thenSource">Sequence to return in case the condition evaluates true.</param> /// <param name="elseSource">Sequence to return in case the condition evaluates false.</param> /// <returns>Either of the two input sequences based on the result of evaluating the condition.</returns> public static IEnumerable<TResult> If<TResult>(Func<bool> condition, IEnumerable<TResult> thenSource, IEnumerable<TResult> elseSource) { if (condition == null) throw new ArgumentNullException("condition"); if (thenSource == null) throw new ArgumentNullException("thenSource"); if (elseSource == null) throw new ArgumentNullException("elseSource"); return EnumerableEx.Defer(() => condition() ? thenSource : elseSource); } /// <summary> /// Returns an enumerable sequence if the evaluation result of the given condition is true, otherwise returns an empty sequence. /// </summary> /// <typeparam name="TResult">Result sequence element type.</typeparam> /// <param name="condition">Condition to evaluate.</param> /// <param name="thenSource">Sequence to return in case the condition evaluates true.</param> /// <returns>The given input sequence if the condition evaluates true; otherwise, an empty sequence.</returns> public static IEnumerable<TResult> If<TResult>(Func<bool> condition, IEnumerable<TResult> thenSource) { if (condition == null) throw new ArgumentNullException("condition"); if (thenSource == null) throw new ArgumentNullException("thenSource"); return EnumerableEx.Defer(() => condition() ? thenSource : Enumerable.Empty<TResult>()); } /// <summary> /// Generates an enumerable sequence by repeating a source sequence as long as the given loop postcondition holds. /// </summary> /// <typeparam name="TResult">Result sequence element type.</typeparam> /// <param name="source">Source sequence to repeat while the condition evaluates true.</param> /// <param name="condition">Loop condition.</param> /// <returns>Sequence generated by repeating the given sequence until the condition evaluates to false.</returns> public static IEnumerable<TResult> DoWhile<TResult>(this IEnumerable<TResult> source, Func<bool> condition) { if (source == null) throw new ArgumentNullException("source"); if (condition == null) throw new ArgumentNullException("condition"); return source.Concat(While(condition, source)); } /// <summary> /// Returns a sequence from a dictionary based on the result of evaluating a selector function. /// </summary> /// <typeparam name="TValue">Type of the selector value.</typeparam> /// <typeparam name="TResult">Result sequence element type.</typeparam> /// <param name="selector">Selector function used to pick a sequence from the given sources.</param> /// <param name="sources">Dictionary mapping selector values onto resulting sequences.</param> /// <returns>The source sequence corresponding with the evaluated selector value; otherwise, an empty sequence.</returns> public static IEnumerable<TResult> Case<TValue, TResult>(Func<TValue> selector, IDictionary<TValue, IEnumerable<TResult>> sources) { if (selector == null) throw new ArgumentNullException("selector"); if (sources == null) throw new ArgumentNullException("sources"); return Case(selector, sources, Enumerable.Empty<TResult>()); } /// <summary> /// Returns a sequence from a dictionary based on the result of evaluating a selector function, also specifying a default sequence. /// </summary> /// <typeparam name="TValue">Type of the selector value.</typeparam> /// <typeparam name="TResult">Result sequence element type.</typeparam> /// <param name="selector">Selector function used to pick a sequence from the given sources.</param> /// <param name="sources">Dictionary mapping selector values onto resulting sequences.</param> /// <param name="defaultSource">Default sequence to return in case there's no corresponding source for the computed selector value.</param> /// <returns>The source sequence corresponding with the evaluated selector value; otherwise, the default source.</returns> public static IEnumerable<TResult> Case<TValue, TResult>(Func<TValue> selector, IDictionary<TValue, IEnumerable<TResult>> sources, IEnumerable<TResult> defaultSource) { if (selector == null) throw new ArgumentNullException("selector"); if (sources == null) throw new ArgumentNullException("sources"); if (defaultSource == null) throw new ArgumentNullException("defaultSource"); return EnumerableEx.Defer(() => { IEnumerable<TResult> result; if (!sources.TryGetValue(selector(), out result)) result = defaultSource; return result; }); } /// <summary> /// Generates a sequence by enumerating a source sequence, mapping its elements on result sequences, and concatenating those sequences. /// </summary> /// <typeparam name="TSource">Source sequence element type.</typeparam> /// <typeparam name="TResult">Result sequence element type.</typeparam> /// <param name="source">Source sequence.</param> /// <param name="resultSelector">Result selector to evaluate for each iteration over the source.</param> /// <returns>Sequence concatenating the inner sequences that result from evaluating the result selector on elements from the source.</returns> public static IEnumerable<TResult> For<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, IEnumerable<TResult>> resultSelector) { if (source == null) throw new ArgumentNullException("source"); if (resultSelector == null) throw new ArgumentNullException("resultSelector"); return ForCore(source, resultSelector).Concat(); } static IEnumerable<IEnumerable<TResult>> ForCore<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, IEnumerable<TResult>> resultSelector) { return source.Select(resultSelector); } } }