Extension methods ngidini sampeyan "nambah" methods menyang type sing ana (kalebu type sing ora sampeyan duwe, kaya string utawa int) tanpa ngowahi utawa turun-temurun. Padha ditetepake minangka static methods kanthi this modifier ing parameter pisanan, lan dipanggil kaya method instance. LINQ dibangun ing dhuwur padha.
public static class StringExtensions
{
// `this string str` makes this an extension method ON string
public static bool IsValidEmail(this string str)
{
return str.Contains("@") && str.Contains(".");
}
public static string Truncate(this string str, int max)
{
return str.Length <= max ? str : str[..max] + "...";
}
}
// call them as if they were instance methods on string
"[email protected]".IsValidEmail(); // true
"long text here".Truncate(5); // "long ..."
Modifier this ing parameter pisanan nandai method minangka extension saka type kasebut. Iku static method, nanging sampeyan manggil kaya method instance (str.IsValidEmail()), sing maca alami.
// these are equivalent — the extension call is sugar for a static call
"[email protected]".IsValidEmail();
StringExtensions.IsValidEmail("[email protected]");
Extension methods iku compiler magic — padha tenan static method calls, nanging this-parameter syntax ngidini sampeyan manggil padha fluently kaya yen padha duwé type. (Padha kudu ana ing static class lan namespace diimpor kanthi using.)
// Where, Select, OrderBy, etc. are extension methods on IEnumerable<T>
list.Where(x => x > 0).Select(x => x * 2);
// → IEnumerable<T> has no Where method; LINQ ADDS them via extension methods
Semua operator query LINQ (Where, Select, mbl.) minangka extension methods ing IEnumerable<T> — iki alasan kenapa padha chain saengga fluent. Iki minangka panggunaan sing paling menonjol saka extension methods.
Extension methods minangka feature C# sing penting lan khas, lan ngerti padha penting kanggo nggunakake padha lan ngerti carane bagean kunci C# gumana — paling biasane LINQ, sing kabeh dibangun ing extension methods (operator Where/Select/OrderBy minangka extension ing IEnumerable<T>, iki alasan kenapa padha chain saengga fluent).
Feature iki ngidini sampeyan nambah functionality menyang type sing ana — kalebu sing ora sampeyan duwe (string, int, framework types) utawa ora bisa diowahi (sealed classes, interfaces) — tanpa inheritance utawa ngowahi original, nalika njaga clean, fluent calling syntax (str.IsValidEmail() maca kaya method instance).
Iku migunani kanggo nulis helper methods sing extend types alami, mbangun fluent APIs, lan nambah behavior menyang interfaces.
Ngerti extension methods — carane mendefinisikake padha (this ing parameter pisanan, ana ing static class), yen padha syntactic sugar kanggo static calls, lan terutama yen LINQ dibangun ing padha — minangka pengetahuan penting kanggo nulis clean, fluent C# helpers lan ngerti carane LINQ lan akeh fluent .NET APIs oleh syntax padha.
Sanajan extension methods ndasari salah sawijining feature C# sing paling penting (LINQ) lan minangka cara umum kanggo extend types kanthi elegan, ngerti padha minangka frequently-applied knowledge sing bisa nunjukake ngerti carane fluent, extensible APIs C# gumana — lan ngidini sampeyan nulis code sing padha clean, discoverable.