Implement shortened methods with => syntax

src/dmd/cli.d

@@ -792,6 +792,8 @@ dmd -cov -unittest myprog.d
             "`in` on parameters means `scope const [ref]` and accepts rvalues"),
         Feature("inclusiveincontracts", "inclusiveInContracts",
             "'in' contracts of overridden methods must be a superset of parent contract"),
+        Feature("shortenedMethods", "shortenedMethods",
+            "allow use of => for methods and top-level functions in addition to lambdas"),
         // DEPRECATED previews
         // trigger deprecation message once D repositories don't use this flag anymore
         Feature("markdown", "markdown", "enable Markdown replacements in Ddoc", false, false),

src/dmd/frontend.h

@@ -7033,6 +7033,7 @@ struct Param
     bool useExceptions;
     bool noSharedAccess;
     bool previewIn;
+    bool shortenedMethods;
     bool betterC;
     bool addMain;
     bool allInst;
@@ -7173,6 +7174,7 @@ struct Param
         useExceptions(true),
         noSharedAccess(),
         previewIn(),
+        shortenedMethods(),
         betterC(),
         addMain(),
         allInst(),

src/dmd/globals.d

@@ -190,6 +190,7 @@ extern (C++) struct Param
     bool useExceptions = true;   // support exception handling
     bool noSharedAccess;         // read/write access to shared memory objects
     bool previewIn;         // `in` means `[ref] scope const`, accepts rvalues
+    bool shortenedMethods; // allow => in normal function declarations
     bool betterC;           // be a "better C" compiler; no dependency on D runtime
     bool addMain;           // add a default main() function
     bool allInst;           // generate code for all template instantiations

src/dmd/globals.h

@@ -170,6 +170,7 @@ struct Param
     bool useExceptions; // support exception handling
     bool noSharedAccess; // read/write access to shared memory objects
     bool previewIn;     // `in` means `scope const`, perhaps `ref`, accepts rvalues
+    bool shortenedMethods; // allow => in normal function declarations
     bool betterC;       // be a "better C" compiler; no dependency on D runtime
     bool addMain;       // add a default main() function
     bool allInst;       // generate code for all template instantiations

src/dmd/parse.d

@@ -848,7 +848,7 @@ final class Parser(AST) : Lexer
                 Token* tk;
                 if (token.value == TOK.identifier && skipParens(peek(&token), &tk) && skipAttributes(tk, &tk) &&
                     (tk.value == TOK.leftParentheses || tk.value == TOK.leftCurly || tk.value == TOK.in_ ||
-                     tk.value == TOK.out_ || tk.value == TOK.do_ ||
+                     tk.value == TOK.out_ || tk.value == TOK.do_ || tk.value == TOK.goesTo ||
                      tk.value == TOK.identifier && tk.ident == Id._body))
                 {
                     version (none)
@@ -4753,7 +4753,7 @@ final class Parser(AST) : Lexer
                 Token* tk;
                 if ((storage_class || udas) && token.value == TOK.identifier && skipParens(peek(&token), &tk) &&
                     skipAttributes(tk, &tk) &&
-                    (tk.value == TOK.leftParentheses || tk.value == TOK.leftCurly || tk.value == TOK.in_ || tk.value == TOK.out_ ||
+                    (tk.value == TOK.leftParentheses || tk.value == TOK.leftCurly || tk.value == TOK.in_ || tk.value == TOK.out_ || tk.value == TOK.goesTo ||
                      tk.value == TOK.do_ || tk.value == TOK.identifier && tk.ident == Id._body))
                 {
                     version (none)
@@ -5119,6 +5119,18 @@ final class Parser(AST) : Lexer
     L1:
         switch (token.value)
         {
+        case TOK.goesTo:
+            if (requireDo)
+                error("missing `do { ... }` after `in` or `out`");
+            if (!global.params.shortenedMethods)
+                error("=> shortened method not enabled, compile with compiler switch `-preview=shortenedMethods`");
+            const returnloc = token.loc;
+            nextToken();
+            f.fbody = new AST.ReturnStatement(returnloc, parseExpression());
+            f.endloc = token.loc;
+            check(TOK.semicolon);
+            break;
+
         case TOK.leftCurly:
             if (requireDo)
                 error("missing `do { ... }` after `in` or `out`");

test/compilable/previewhelp.d

@@ -17,5 +17,6 @@ Upcoming language changes listed by -preview=name:
   =nosharedaccess   disable access to shared memory objects
   =in               `in` on parameters means `scope const [ref]` and accepts rvalues
   =inclusiveincontracts 'in' contracts of overridden methods must be a superset of parent contract
+  =shortenedMethods allow use of => for methods and top-level functions in addition to lambdas
 ----
 */

test/compilable/shortened_methods.d

@@ -0,0 +1,33 @@
+// REQUIRED_ARGS: -preview=shortenedMethods
+class A {
+    int _x = 34;
+    // short syntax works in all contexts
+    @property x() => _x;
+    @property x(int v) => _x = v;
+
+    // including with contracts
+    @property y() in(true) => _x;
+
+    // or other auto returns
+    auto foo() @safe => assert(0);
+
+    // or normal method defintions
+    bool isNull() => this is null;
+}
+
+class B : A{
+    // short syntax also overrides the same as long syntax
+    override bool isNull() => this !is null;
+}
+
+static assert((new A).x == 34);
+
+string test() => "hello"; // works at any scope
+
+static assert(test() == "hello"); // works normally
+static assert(is(typeof(&test) == string function())); // same normal type
+
+void func() {
+    int a;
+    int nested() => a; // and at nested scopes too
+}