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8934 :: A constant reference/alias or pointer jut like as it is of C++ parameter

• mardiyah (orginal) [2022-02-19T01:00:54+01:00] view original

  How to have constant reference/alias or pointer as it's parameter analogue on either

  
  foo( int const * aPointer,   const int & aliasVariable) {   // ... 
  Run

  C++ parameter syntax

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• demotomohiro (orginal) [2022-02-19T01:27:10+01:00] view original

  In default, parameters are immutable in Nim. Unlike C/C++, Nim doesn't have const type qualifier. Mutability is an attribute of symbol, not type.

  Please read the Note in end of this section. https://nim-lang.github.io/Nim/manual.html#procedures-var-parameters

  If you want immutable ref type: https://nim-lang.org/docs/manual_experimental.html#strict-funcs

  If you want to define pointer parameters to declare C or C++ functions, you can use ptr int type but Nim doesn't have const pointer type.

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• sls1005 (orginal) [2022-02-19T04:28:56+01:00] view original

  var foo {.codegenDecl: "const $1 $2".}: ptr cint #const int * foo

  Run

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• mardiyah (orginal) [2022-02-19T08:41:24+01:00] view original

  I'm honestly noob in Nim, it's so encouraged to detail answer to an explanatory expressions

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• sls1005 (orginal) [2022-02-19T09:58:28+01:00] view original

  const is a keyword in Nim. So we can't simply define:

  type ConstInt = const int #error
  Run

  But we can import it. When translated into C, Nim int is defined as NI, so we can import const NI.

  type ConstInt {.importc: "const NI".} = int
  Run

  After that, ptr ConstInt in Nim will become const NI* in C.

  In C++, alias type of Nim int is NI&, so we can import const NI&.

  type ConstIntAlias {.importc: "const NI&".} = int
  Run

  And then foo(int const * aPointer, const int & aliasVariable) can be defined as

  proc foo(aPointer: ptr ConstInt, aliasVariable: ConstIntAlias) =
    discard
  Run

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• mardiyah (orginal) [2022-02-19T16:43:40+01:00] view original

  I just know that Nim can't be as C++ way

  so do we think the alias one would work, how'd it actually happen runtime error ?

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• sls1005 (orginal) [2022-02-20T06:34:00+01:00] view original

  In Nim, const int is a compile time error. But it's OK to import from C.

  type
    ConstInt {.importc: "const NI".} = int
    ConstCInt {.importc: "const int".} = cint
  Run

  They can be used for parameters or pointers.

  var p: ptr ConstCInt
  #is translated to:
    #const int * p;
  Run

  But not variables.

  var x: ConstCInt = 1 #invalid
  #is translated to:
    #const int x;
    #x = 1;
  Run

  Alias can also be imported from C++, and used for parameters.

  type
    IntAlias {.importcpp: "NI&".} = int
    CIntAlias {.importcpp: "int&".} = cint
  Run

  But it's meaningless since parameters are immutable.

  proc foo(x: IntAlias) =
    x += 1 #error
  Run

  We cannot define alias variables.

  var
    x: cint = 1
    y: CIntAlias = x #invalid
  #is translated to:
    #int x;
    #int& y;
    #y = x;
  Run

  The only usage seem to be interfacing with C or C++.

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