ntrel · HackerTrans

11 месяцев назадdiscuss

My understanding is that RC is relatively expensive in time (especially for atomic RC) but uses a lot less memory than state of the art fast GC. And RC doesn't handle cycles.

ntrel

4 года назадdiscuss

D doesn't store capacity in each slice. This allows a slice to fit in registers more often. Instead for GC allocated slices, the GC will store metadata before the first element of the allocation. That does make it slower to access, particularly when the slice points past the first element, but it is cached to speed up repeated accesses to the same allocation. Repeated appending can be further speeded up by using a dedicated Appender type.

ntrel

4 года назадdiscuss

Because Go designers don't like OOP and didn't want low-level system programming as core features. They also were not keen on generic programming. Basically they wanted a simpler language. (Then they realized generics are useful, ironically their constraints add complexity). Also they wanted a segmented stack and coroutines + channels as language features.

ntrel

4 года назадdiscuss

This compiles:

    ref ubyte[n*2] requires_ptr_twice_as_large_as_input(uint n)
    (
        const ref ubyte[n] input,
        ref ubyte[n*2] output,
    ) {
        output[0..n] = input[0..n];
        output[n..2*n] = input[0..n];
        return output;
    }

    void main()
    {
        ubyte[10] input = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
        ubyte[20] output;
        requires_ptr_twice_as_large_as_input!(10)(input, output);

        import std.stdio;
        writeln(output);
        assert(output == input ~ input);
    }

ntrel

4 года назадdiscuss

Why is your proposal better than this:

  import std.sumtype;
  
  void main(){
   struct A { int a; }
   struct B { string b; }
   struct C { bool c; }
   
   alias TaggedUnion = SumType!(A, B, C);
   
   auto tgu = TaggedUnion(B("hi"));
   int i = tgu.match!(
    (A a) => a.a,
    (B b) => b.b.length,
    (C c) => c.c * 5
   );
   assert(i == 2);
  }

If you miss out a `match` handler for any of A, B, C you get a compile-time error. Or you can use a generic handler which will be instantiated for any type not explicitly handled. https://dlang.org/phobos/std_sumtype.html

ntrel

4 года назадdiscuss

Class instances can go on the stack too using `scope`:

  scope obj = new Object;
  ...
  // destroyed at end of scope

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