vendor/github.com/zclconf/go-cty/cty/function/unpredictable.go

   1 package function
   2
   3 import (
   4         "github.com/zclconf/go-cty/cty"
   5 )
   6
   7 // Unpredictable wraps a given function such that it retains the same arguments
   8 // and type checking behavior but will return an unknown value when called.
   9 //
  10 // It is recommended that most functions be "pure", which is to say that they
  11 // will always produce the same value given particular input. However,
  12 // sometimes it is necessary to offer functions whose behavior depends on
  13 // some external state, such as reading a file or determining the current time.
  14 // In such cases, an unpredictable wrapper might be used to stand in for
  15 // the function during some sort of prior "checking" phase in order to delay
  16 // the actual effect until later.
  17 //
  18 // While Unpredictable can support a function that isn't pure in its
  19 // implementation, it still expects a function to be pure in its type checking
  20 // behavior, except for the special case of returning cty.DynamicPseudoType
  21 // if it is not yet able to predict its return value based on current argument
  22 // information.
  23 func Unpredictable(f Function) Function {
  24         newSpec := *f.spec // shallow copy
  25         newSpec.Impl = unpredictableImpl
  26         return New(&newSpec)
  27 }
  28
  29 func unpredictableImpl(args []cty.Value, retType cty.Type) (cty.Value, error) {
  30         return cty.UnknownVal(retType), nil
  31 }