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7052 :: conditional expressions don't work in a formatted string

• HJarausch (orginal) [2020-11-08T13:48:56+01:00] view original

  Unless I am missing something, the following Python-alike doesn't work

  import strformat
  let x=1
  echo fmt"{if x > 0 : 7 else: 0}"
  Run

  neither does

  echo fmt"{(if x > 0 : 7 else: 0)}"
  Run

  Is this a feature? Is there a simple workaround?

  Thanks for a hint, Helmut

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• jrfondren (orginal) [2020-11-08T13:56:18+01:00] view original

  This works:

  
  echo &"{[0,7][int(x > 7)]}"
  Run

  I imagine the restriction is related to the {} format options that all involve colons (:), which are a feature. What I would actually do is assign a variable to the result of that conditional.

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• cblake (orginal) [2020-11-08T13:56:19+01:00] view original

  See this thread. I think it would not be hard to modify the embedded inline parser in strformat to allow internal :, and this has come up often enough that it might be a good first PR...

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• pietroppeter (orginal) [2020-11-08T13:58:45+01:00] view original

  Expressions containing ‘:’ do not work, see here: https://stackoverflow.com/questions/63602254/how-can-i-use-expression-inside-formatted-string-in-nim

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• xigoi (orginal) [2020-11-09T00:21:39+01:00] view original

  Maybe you could use the ternary operator from Elvis?

  echo fmt"{(x > 0) ? 7 ! 0}"
  Run

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• HJarausch (orginal) [2020-11-11T13:25:44+01:00] view original

  Many thanks. I think that's a good candidate for Nim proper.

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• timothee (orginal) [2021-04-15T04:12:41+02:00] view original

  this works:

  import std/strformat
  let x = 3.14
  assert fmt"{(if x!=0: 1.0/x else: 0):.5}" == "0.31847"
  assert fmt"{(if true: 1 else: 2)}" == "1"
  assert fmt"{if true\: 1 else\: 2}" == "1"
  Run

  and avoids conflicts with format specifier. See https://github.com/nim-lang/Nim/pull/17700 for more details.

  (same answer as https://stackoverflow.com/a/67101278/1426932)

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• shirleyquirk (orginal) [2021-04-15T15:14:11+02:00] view original

  please try to break it! i'm sure there's edge cases I haven't found

  curly brackets can also be used, backslash escaped, so that table/json constructors can be used:

  import tables,strformat
  let (foo,bar) = (3,4)
  assert&"""{ toTable( \{"foo": foo, "bar": bar \} ) }""" == """{"foo": 3, "bar": 4}"""
  Run

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