How can I use a dynamic format string with the format! macro?

Question

I want to use the format! macro with a String as first argument, but because the macro expects a string literal, I am not able pass anything differ

Answer 1

Check out the strfmt library, it is the closest I've found to do dynamic string formatting.

Answer 2

Short answer: it cannot be done.

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Long answer: the format! macro (and its derivatives) requires a string literal, that is a string known at compilation-time. In exchange for this requirement, if the arguments provided do not match the format, a compilation error is raised.

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What you are looking for is known as a template engine. A non-exhaustive list of Rust template engines in no particular order:

• Handlebars
• Rustache
• Maud
• Horrorshow
• fomat-macros
• ...

Template engines have different characteristics, and notably differ by the degree of validation occurring at compile-time or run-time and their flexibility (I seem to recall that Maud was very HTML-centric, for example). It's up to you to find the one most fitting for your use case.