Add record.create, update readme

readme.md

@@ -64,6 +64,9 @@ alias DefaultRecord = record!(
 
 auto r = new DefaultRecord; // run the default initialisers
 writeln(r); // {x = 4, o = object.Object}
+
+auto q = DefaultRecord.create!"x"(9); // run default initialisers, then set x to 9
+writeln(r); // {x = 9, o = object.Object}
 ```
 
 [0]: [Records in C#](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/types/records)

source/drecord.d

@@ -158,6 +158,16 @@ template record(args...)
 
 		mixin(genCtor);
 
+		/// Explicitly set certain fields, default initialise the rest
+		static record create(TNames...)(...)
+		{
+			auto r = new record;
+			import core.vararg;
+			static foreach(item; AliasSeq!TNames)
+				mixin("r." ~ item ~ "_ = va_arg!(typeof(" ~ item ~ "_))(_argptr);");
+			return r;
+		}
+
 		/++ Test for equality. Reference types are checked to ensure
 		+ their references are the same (point to same thing), value types
 		+ are checked to ensure their values are identical.