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3352 :: Can I somehow show context-specific information in an {.error.} ?

• monster (orginal) [2017-11-20T13:21:37+01:00] view original

  I'm trying to debug a compilation problem: the generic parameter of a proc doesn't seem to match my expectation, so I'd like to write something like this:

  let b: byte = 42'u8
  
  proc test*[T](t: T): bool =
    when sizeof(T) == 1:
      result = true # ...
    else:
      {.error: "invalid parameter size: " & $sizeof(T).}
  
  test(b)
  Run

  But the compiler returns this:

  Error: invalid pragma: error: "invalid parameter size: " & $ sizeof(T)
  Run

  I tried searching in the Nim codebase, but found no example. So is it impossible?

  find . -name "*.nim" | xargs fgrep "{.error"
  Run

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• stisa (orginal) [2017-11-20T13:31:05+01:00] view original

  You can use asserts:

  let b: byte = 42'u8
  let c = 42'u16
  proc test*[T](t: T): bool =
    assert(sizeof(T) == 1, "invalid parameter size: " & $sizeof(T))
    result = true
  echo test(b)
  echo test(c)
  Run

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• monster (orginal) [2017-11-20T14:05:22+01:00] view original

  @stisa Actually, I meant "when sizeof(T) == 1" rather than "if sizeof(T) == 1" (now corrected). But the problem is, that in the real code I want to support multiple paramter sizes, and get a compile time error if the size is unexpected. The example you gave me compiles, but fails at runtime. OTOH, this led me to find that I can has static asserts (static: assert(false, "invalid parameter size: " & $sizeof(T))), and that does the trick. Still, it would be nice if the error pragma supported that too.

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• stisa (orginal) [2017-11-20T14:27:59+01:00] view original

  Mmh there is an error proc in macros that I think does that: https://nim-lang.org/docs/macros.html#error,string,NimNode

  edit: Nope, the proc only works in compile time contexts

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