Re: initializing struct containing user defined type
On Friday, 18 February 2022 at 23:46:51 UTC, forkit wrote: On Friday, 18 February 2022 at 16:45:24 UTC, Ali Çehreli wrote: ... I think that syntax will be obviated when D will have named arguments. Ali Huh? D doesn't have named arguments, already? That's an important component for safe(r) programming. Do you know if there is a DIP for this, and if so, it's current status. The DIP is [accepted] but not implemented. [accepted]: https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1030.md
Re: initializing struct containing user defined type
On Friday, 18 February 2022 at 16:45:24 UTC, Ali Çehreli wrote: ... I think that syntax will be obviated when D will have named arguments. Ali Huh? D doesn't have named arguments, already? That's an important component for safe(r) programming. Do you know if there is a DIP for this, and if so, it's current status.
Re: initializing struct containing user defined type
On 2/18/22 12:16, Salih Dincer wrote: >// x.writeln(y); // 2.087 >"D Compiler v".writeln(__VERSION__/1000.0); > ``` > I'm using v2.087 but because of @disable this line doesn't work: ```// > x.writeln(y); // 2.087``` > > Why? Can you give an explanation for this? This is not related to struct initialization. The issue can be reduced to the following: struct S { @disable this(this); } void foo(S s) { } void main() { auto s = S(); foo(s); } Error: struct `deneme.S` is not copyable because it has a disabled postblit foo takes by-value but S disables copying. The same thing happens with your example inside a Phobos function: void write(S...)(S args) { // ... foreach (arg; args) // ... } foreach iterates the arguments by-value there. Same issue. Ali
Re: initializing struct containing user defined type
On Friday, 18 February 2022 at 16:45:24 UTC, Ali Çehreli wrote: On 2/18/22 07:01, kdevel wrote: > Error: struct `B` has constructors, cannot use `{ initializers }`, > use `B( initializers )` instead > > What is the rationale behind that? I mean: If the compiler exactly > sees what the program author intends to express why does it force the > author to change the code? I don't know the answer to that. The {} initializers always seemed out of place to me. I assumed they had to be supported to copy+paste C code to D and it should mostly work. One benefit of the {} initializer is being able use named initializers: struct S { int a; int b; } void main() { S s = { b : 2, a : 1 }; } I still think it's out of place. :) I think that syntax will be obviated when D will have named arguments. Ali ```d struct S { float a, b; @disable this(this); } enum par : float { a = 1, b = 2 } S x = { b : par.b, a : par.a }; S y = S(par.a, par.b); auto s1 = x.a / x.b; auto s2 = y.a / y.b; s1.writeln(); s2.writeln(); writeln(s1 + s2); // x.writeln(y); // 2.087 "D Compiler v".writeln(__VERSION__/1000.0); ``` I'm using v2.087 but because of @disable this line doesn't work: ```// x.writeln(y); // 2.087``` Why? Can you give an explanation for this?
Re: initializing struct containing user defined type
On 2/18/22 07:01, kdevel wrote: > Error: struct `B` has constructors, cannot use `{ initializers }`, > use `B( initializers )` instead > > What is the rationale behind that? I mean: If the compiler exactly > sees what the program author intends to express why does it force the > author to change the code? I don't know the answer to that. The {} initializers always seemed out of place to me. I assumed they had to be supported to copy+paste C code to D and it should mostly work. One benefit of the {} initializer is being able use named initializers: struct S { int a; int b; } void main() { S s = { b : 2, a : 1 }; } I still think it's out of place. :) I think that syntax will be obviated when D will have named arguments. Ali
Re: initializing struct containing user defined type
On Friday, 18 February 2022 at 14:37:25 UTC, Ali Çehreli wrote: On 2/18/22 06:19, kdevel wrote: > // auto b3 = B ("A", "B"); // Error: cannot implicitly convert > // expression `"A"` of type `string` to `A` Yeah, D disallows some implicit conversions. Adding a constructor to B will make it work: this(string as, string bs) { this.a = A(as); this.b = A(bs); } } Okay. b0 needs an additional constructor with signature this (A, A). The initialization of b3 is now no longer working. dmd says: Error: struct `B` has constructors, cannot use `{ initializers }`, use `B( initializers )` instead What is the rationale behind that? I mean: If the compiler exactly sees what the program author intends to express why does it force the author to change the code?
Re: initializing struct containing user defined type
On 2/18/22 06:19, kdevel wrote: > // auto b3 = B ("A", "B"); // Error: cannot implicitly convert > // expression `"A"` of type `string` to `A` Yeah, D disallows some implicit conversions. Adding a constructor to B will make it work: this(string as, string bs) { this.a = A(as); this.b = A(bs); } } Ali
initializing struct containing user defined type
Instead of using string I want to use A in the definition of B: struct A { string s; this (string s) { this.s = s; } } struct B { A a; A b; } Alas I have some difficulty initializing a B in the accustomed manner (b3): void main () { auto b0 = B (A ("A"), A ("B")); // as expected but I don't want // to change the client code // B b1 = { {"A"}, {"B"} }; // works if A has no (explicit) ctor // but I don't want to write the braces B b2 = {"A", "B"}; // works but why? // auto b3 = B ("A", "B"); // Error: cannot implicitly convert // expression `"A"` of type `string` to `A` } Hasn't this been treated here before?