Bug 1547 – Default parameter values should use implicit static opCall

For the most part it's possible to make a struct that wraps an array act like a built-in array. However it's not possible to give a default value of null to a struct. I think the code below should probably call the static opCall for foo(). module structnull; import std.stdio; struct Struct { int[] data; static Struct opCall(int[] d) { writefln("static opCall"); Struct ret; ret.data = d; return ret; } void opAssign(int[] d) { writefln("opAssign"); Struct ret; ret.data = d; return ret; } int opEquals(int[] d) { writefln("opEquals"); return d==data; } } // this gives // structnull.d(37): Error: cannot implicitly convert expression (null) of type void* to Struct void foo(Struct s = null) { } void main() { Struct a = null; // ok opCall a = null; // ok opAssign if (a == null) { // op opEquals writefln("yep"); } }

This bug does not only apply to null as a default parameter, but in every case where a struct OR class should get initialized by another type. To point out the importance of this issue, I'd like to mention the application of a GMP wrapper library which wraps the GMP types (from the C library) in structs and expression templates. For GMP it is important that one can use these structs like native datatypes: void foo (mpz arg = 0) { ... } one may argue, that you can write "arg = T(0)" (via static opCall), but this does not work for int, so using mpz like int would not work! best regards Matthias Walter

@RazvanN7 created dlang/dmd pull request #10329 "Fix Issue 1547 - Default parameter values should use implicit static opCall" fixing this issue: - Fix Issue 1547 - Default parameter values should use implicit static opCall https://github.com/dlang/dmd/pull/10329

dlang/dmd pull request #10329 "Fix Issue 1547 - Default parameter values should use implicit static opCall" was merged into master: - 1b552a67a1d205ff2747897d0934c922a869e25e by RazvanN7: Fix Issue 1547 - Default parameter values should use implicit static opCall https://github.com/dlang/dmd/pull/10329

(In reply to Bill Baxter from comment #0) > void foo(Struct s = null) Nice that this is now allowed, is it possible to also allow calling foo(null)? Then structs could be a drop-in replacement for pointers, but doing some extra checks on certain operations.