Unexpected behavior of evaluating "index" in "test.Ternary"

[rmrnc]

Hi
Maybe it's just me, but somehow the semantic of gomplate's test.Ternary processing the result of index eludes me.

$ gomplate --version

gomplate version 4.1.0

$ echo '{ "key": "value"  }' | gomplate --context .=stdin:///in.json \
    --in '{{ index . "key" | ternary (index . "key") (printf "unexpected %s" (index . "key")) }}'

unexpected value

$ echo '{ "key": "value"  }' | gomplate --context .=stdin:///in.json \
    --in '{{ index . "not_a_key" | ternary (index . "not_a_key") "expected" }}'

expected                                               

Especially, when compared to

echo '{ "key": "value"  }' | gomplate --context .=stdin:///in.json \
    --in '{{ $x := "initial" }}{{ if (index . "key") }}{{ $x = (index . "key") }}{{ else }}{{ $x = "default" }}{{ end }} x={{ $x }}'

x=value

echo '{ "key": "value"  }' | gomplate --context .=stdin:///in.json \
    --in '{{ $x := "initial" }}{{ if (index . "not_a_key") }}{{ $x = (index . "key") }}{{ else }}{{ $x = "default" }}{{ end }} x={{ $x }}'

x=default

Would you mind pointing out where I went wrong?

Thank you very much

[hairyhenderson]

It may just be an over-simple example, but why are you using index when you could just refer to the item by .key?

One other issue here is that the test.Ternary expects a boolean (or boolean-like string), so feeding it "value" is indeed going to cause confusion.

The reason the second example works is that the if keyword is much broader in scope - given a non-boolean value it'll consider any non-empty value to be true. I suppose the documentation is somewhat misleading:

This is effectively a short-form of the following template:

the word "effectively" does a lot of heavy lifting there, as what I really meant was "this is similar in concept, but with subtle and very important differences" 🤦‍♂️

Perhaps simply removing that block would reduce confusion...

[rmrnc]

Sorry, for my late reply.

why are you using index when you could just refer to the item by .key?

Unfortunately, the clumsy use of index is due to the fact, that if a key does not exist, referring to it results in an map has no entry for key error.

I suppose the documentation is somewhat misleading

I am afraid, I have to agree.

Still worse, trying to apply test.Ternary for some sort of "nil-coalescing", forces an arguably cumbersome

{{ (ne (index . "key") "") | ternary .key "some default" }}

expression. What is your take on providing a dedicated operator/function for this common situation in gomplate?

[rmrnc]

Just realized, that

'{{ (has . "key") | ternary .key "some default" }}

provides a more palatable option. I guess, that's as good as it gets.