undefined | Better HN

0 pointsWalterBright4y ago0 comments

> I really don’t understand why they are not allowed.

I don't, either. Such were in D from 2000 or so.

I also don't understand why `class` in C++ sits in the tag name space. I wrote Bjarne in the 1980s asking him to remove it from the tag name space, as the tag name space is an abomination. He replied that there was too much water under that bridge.

D doesn't have the tag name space, and in 20 years not a single person has asked for it.

This did cause some trouble for me with ImportC to support things like:

    struct S { ... };
    int S;

but I found a way. Although such code is an abomination. I've only seen it in the wild in system .h files.

0 comments

Gibbon14y ago

The only explanation I saw was that C++ standards guys were horrified by the idea of unpredictable side effects as a result of initialization of a struct.

I think C++ though is adding them.

What I'd like in c is designated function parameters.

  // these the same
  bar(.a = 10, .b = 12);
  bar(.b = 12, .a = 10);

saagarjha4y ago

I suspect that to many C++ programmers, most initializations of structs have unpredictable side effects because of how complex they are ;)

wott4y ago

You can somewhat fake it by replacing your functions parameters list with a single struct parameter.

    struct bar_arguments {
       int a, b;
    };
    int bar(struct bar_arguments args) { return 2*args.a + args.b;}

    #define bar(...) bar((struct bar_arguments) {__VA_ARGS__})

    // usage (will print 32 three times)
    printf("%d\n", bar(10, 12));
    printf("%d\n", bar(.a = 10, .b = 12));
    printf("%d\n", bar(.b = 12, .a = 10));

The main drawback is that all parameters are now optional: it will not complain if you forget to assign all parameters, it will silently set them to 0 :-/

    printf("%d\n", bar(10));
    printf("%d\n", bar(.a = 10));
    printf("%d\n", bar(.b = 12));

will print 20, 20 and 12.

You can change those "default values", but then calling the function with regular positional parameters is impaired :-/

gumby4y ago

> The only explanation I saw was that C++ standards guys were horrified by the idea of unpredictable side effects as a result of initialization of a struct.

I don't understand. How would struct or class initialization be any different from simply doing, say, `for (auto& a : { x, y, z }) frob (a);` which is perfectly legal?

Gibbon14y ago

I didn't mention. I think the thought was with designated initializers the order of initialization is what? The order of the elements of the struct? Or the order where it's initialized. In C probably matters little as side effects are usually blatant. C++ I think cryptic side effects are common.

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0 pointsWalterBright4y ago0 comments

> I really don’t understand why they are not allowed.

I don't, either. Such were in D from 2000 or so.

D doesn't have the tag name space, and in 20 years not a single person has asked for it.

This did cause some trouble for me with ImportC to support things like:

    struct S { ... };
    int S;

but I found a way. Although such code is an abomination. I've only seen it in the wild in system .h files.

0 comments

Gibbon14y ago

The only explanation I saw was that C++ standards guys were horrified by the idea of unpredictable side effects as a result of initialization of a struct.

I think C++ though is adding them.

What I'd like in c is designated function parameters.

  // these the same
  bar(.a = 10, .b = 12);
  bar(.b = 12, .a = 10);

saagarjha4y ago

I suspect that to many C++ programmers, most initializations of structs have unpredictable side effects because of how complex they are ;)

wott4y ago

You can somewhat fake it by replacing your functions parameters list with a single struct parameter.

    struct bar_arguments {
       int a, b;
    };
    int bar(struct bar_arguments args) { return 2*args.a + args.b;}

    #define bar(...) bar((struct bar_arguments) {__VA_ARGS__})

    // usage (will print 32 three times)
    printf("%d\n", bar(10, 12));
    printf("%d\n", bar(.a = 10, .b = 12));
    printf("%d\n", bar(.b = 12, .a = 10));

The main drawback is that all parameters are now optional: it will not complain if you forget to assign all parameters, it will silently set them to 0 :-/

    printf("%d\n", bar(10));
    printf("%d\n", bar(.a = 10));
    printf("%d\n", bar(.b = 12));

will print 20, 20 and 12.

You can change those "default values", but then calling the function with regular positional parameters is impaired :-/

gumby4y ago

> The only explanation I saw was that C++ standards guys were horrified by the idea of unpredictable side effects as a result of initialization of a struct.

I don't understand. How would struct or class initialization be any different from simply doing, say, `for (auto& a : { x, y, z }) frob (a);` which is perfectly legal?

Gibbon14y ago

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