jet: Regression: Ranging over slice from Fast Function

I’ve observed a regression caused by https://github.com/CloudyKit/jet/commit/6d666f94dfe73004a23e8e41d7532ac8602c9132 (#112)

Summary

For this template:

{{sorted := SortApples(myApples)}}
{{range i, apple := sorted}}
	{{i}}: {{apple.GetFlavor()}}
{{end}}

(Where SortApples is a fast function aka jet.Func.)

Jet was able to range over the returned slice up until https://github.com/CloudyKit/jet/commit/6d666f94dfe73004a23e8e41d7532ac8602c9132 at which point the template execution would error with: there is no field or method "GetFlavor" in main.Apple

Example Project

https://github.com/tooolbox/jet-example has two branches:

• v2.1.2 (working)
• v2.1.3-6d666f94dfe7 (broken)

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I understand we’re now going for a v3 with these commits, so breaking changes might be expected, but this seems like it would hurt fast functions a lot.

cc @sauerbraten