TODO in assignment pattern

[zzq0119]

Hi Mike, when reading code about assignment pattern , I don't quite understand the meaning of a TODO in PatternExpression.cpp, line 27:

    if (syntax.type) {
        // TODO: allow type references here

Does it mean parameter type or something else? Could you show me an example?

[MikePopoloski]

A type reference is the result of the type operator. This is saying it should be possible to do something like type(some_expression)'{1, 2, 3}

[zzq0119]

module M;
    typedef struct {
        int x;
        int y;
        real radius;
    } ST;
  ST c = '{default: 0, real: 0.0};
   
  ST b =  type(c)'{default: 0, int:1};
endmodule

Has slang already supported such grammar? I parse the example above using slang v0.6 and get no compilation errors. The ast is as follow:

{
  "name": "$root",
  "kind": "Root",
  "addr": 2639652442496,
  "members": [
    {
      "name": "",
      "kind": "CompilationUnit",
      "addr": 2639652668880
    },
    {
      "name": "M",
      "kind": "Instance",
      "addr": 2639652669840,
      "body": {
        "name": "M",
        "kind": "InstanceBody",
        "addr": 2639652669344,
        "members": [
          {
            "name": "ST",
            "kind": "TypeAlias",
            "addr": 2639652669544,
            "target": "struct{int x;int y;real radius;}M.s$1"
          },
          {
            "name": "c",
            "kind": "Variable",
            "addr": 2639652669944,
            "type": {
              "name": "ST",
              "kind": "TypeAlias",
              "addr": 2639652669544,
              "target": "struct{int x;int y;real radius;}M.s$1"
            },
            "initializer": {
              "kind": "StructuredAssignmentPattern",
              "type": {
                "name": "ST",
                "kind": "TypeAlias",
                "addr": 2639652669544,
                "target": "struct{int x;int y;real radius;}M.s$1"
              },
              "constant": "[0,0,0]"
            },
            "lifetime": "Static",
            "isConstant": false,
            "isCompilerGenerated": false
          },
          {
            "name": "b",
            "kind": "Variable",
            "addr": 2639652670080,
            "type": {
              "name": "ST",
              "kind": "TypeAlias",
              "addr": 2639652669544,
              "target": "struct{int x;int y;real radius;}M.s$1"
            },
            "initializer": {
              "kind": "StructuredAssignmentPattern",
              "type": {
                "name": "ST",
                "kind": "TypeAlias",
                "addr": 2639652669544,
                "target": "struct{int x;int y;real radius;}M.s$1"
              },
              "constant": "[1,1,0]"
            },
            "lifetime": "Static",
            "isConstant": false,
            "isCompilerGenerated": false
          }
        ],
        "definition": "M"
      },
      "connections": [
      ]
    }
  ]
}

[MikePopoloski]

It may already work for some cases. The TODO is a note to go back and check that it's fully correct.

[zzq0119]

I have another question in PatternExpression.cpp, line 745

// TODO: check constant index value for validity

I guess it means indexExpr must be constant and the following code is illegal

module M;
  int index=0;
  int cc[int]='{index:1};

  initial $display("%d",cc[0]);
endmodule

But I haven't find any restriction in Chapter 10 or Chapter 7 of IEEE Std 1800-2017 which requires that the item key should be constant. Will any semantic errors be here if non-constant value is used as key?

[MikePopoloski]

It's from the grammar:

array_pattern_key ::= constant_expression | assignment_pattern_key

[zzq0119]

I got it, thanks!