Struct member defaults

[mikex-oss]

What's hard to do? (limit 100 words)

Sometimes you want to specify struct defaults within the struct definition itself.

C++ allows this, e.g.

struct MyStruct
{
    int x;
    int y {};
    int z { 2 };
};

So does SystemVerilog:

  typedef struct {
    logic[31:0] x;
    logic[31:0] y = '0;
    logic[31:0] z = 'd2;
  } my_struct_t;

Rust does not, though see discussion in rust-lang/rfcs#1806.

Current best alternative workaround (limit 100 words)

zero!<MyStruct>() works when everything can be zero-initialized. Otherwise, you can do something like (maybe even later attached to the struct with impl:

fn new_my_struct(x: u32) -> MyStruct {
    MyStruct {
        x: x
        y: u32:0,
        z: u32:2,
    }
}

which is sorta like implementing the Default trait in Rust in that you need to write a separate function that specifies the defaults.

Your view of the "best case XLS enhancement" (limit 100 words)

Even though the Rust RFC languished with mixed opinions, it'd be nice to support this in DSLX for readability and conciseness.

[mikex-oss]

Another pattern I've been using is:

MyStruct {
        x: x,
        ..zero!<MyStruct>()
}

sometimes at multiple levels of hierarchy.

Perhaps a related enhancement is to have some syntactic sugar to fill in the rest of the struct (zero-initialized for now, default-initialized in the future?).