Why does `and` process both expressions if the first one fails?

support
1

I have an if / else if / else statement, if a key isset and has a matching map in a data file, then execute, else fall to the else statement like the following. It works, but it throws error calling index: value is nil; should be of type string.

Why does it process the second expression if the value is not set?

        {{ if .Params.images.thumbnail }}
          <img src="{{ .Params.images.thumbnail }}" class="figure-img img-fluid" alt="{{ .Title }}">
        {{ else if and .Params.images.main (eq .Params.images.main "sectionSlug") }}
          <img src="/images/{{ .Section }}/{{ .Source.BaseFileName }}.jpg" class="figure-img img-fluid" alt="{{ .Title }}">
        {{ else if .Params.images.main }}
          <img src="{{ .Params.images.main }}" class="figure-img img-fluid" alt="{{ .Title }}">
        {{ else if and (isset .Params "ref_key") (index .Site.Data.images .Params.ref_key) }}
          {{ $imgs := index .Site.Data.images .Params.ref_key }}
          <img src="{{ $imgs.Thumbnail.Path }}" class="figure-img img-fluid" alt="{{ .Title }}">
        {{ else }}
          <img src="{{ .Site.Params.image }}" class="figure-img img-fluid" alt="{{ .Title }}">
        {{ end }}
2

As to why, you should ask Rob Pike in Google. I agree that it shouldn’t behave this way, but it’s probably too late to change.

3

So its an issue with Go’s template package?

4

The and operator is standard Go template syntax, so if both the conditions in “and false true” gets evaluated, that is part of Go’s logic.

5

As bep said, this is how the Go templates work right now. The workaround is to do something like this:

{{ else if and (isset .Params "ref_key") (index .Site.Data.images (index .Params "ref_key")) }}
1 Like
6

Interesting, thanks for the workaround. I will give it a shot.