nimforum mirror - Understanding inject pragma

slonik_az (orginal) [2020-10-12T13:58:18+02:00] view original

Hi ALL,

I am trying to understand how inject pragma works and the following behavior is very surprising

let xx = "global xx"

template tt_outer(code: untyped): untyped =
    block:
        let xx {.inject.} = "(tt_outer) xx"
        let yy {.inject.} = "(tt_outer) yy"
        code

template tt_inner(): untyped =
    echo "tt_inner: xx = ", xx
    echo "tt_inner: yy = ", yy

tt_outer:
    tt_inner()

When run, the tt_inner template binds global xx symbol and local yy (as defined in tt_outer) as seen in the output

tt_inner: xx = global xx
tt_inner: yy = (tt_outer) yy

I was expecting both xx and yy bound in the innermost scope. Also, adding mixin xx into tt_inner template definition does not even compile. What am I doing wrong?

--Leo

exelotl (orginal) [2020-10-12T14:58:51+02:00] view original

Hi! I encountered this recently myself too, you can find some discussion and workarounds here:

#15314 Injected symbols aren't resolved properly in expression passed to inner template

The most general fix seems to be using the {.dirty.} pragma:

import macros

let xx = "global xx"

template tt_outer(code: untyped) =
  block:
    let xx {.inject.} = "(tt_outer) xx"
    let yy {.inject.} = "(tt_outer) yy"
    code

template tt_inner() {.dirty.} =
  echo "tt_inner: xx = ", xx
  echo "tt_inner: yy = ", yy

tt_outer:
  tt_inner()

slonik_az (orginal) [2020-10-12T15:15:42+02:00] view original

@exelotl: Thanks a lot!

{.dirty.} solved the problem, indeed. Moreover, when I make both templates "dirty", I do not need {.inject.} any longer.

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6913 :: Understanding inject pragma