Macro expansion, type checking and variable shadowing error

[vron]

Hi,

I am relatively new to rust and am currently trying to translate a structure to rust - but am running into what feels like a bug but probably is a lack of understanding of macros.

The issue is best explained in Rust Playground (rust-lang.org) which is a commented "minimal example".

In short I am trying to write a macro that will let me (efficiently and with clear code) run a closure over a set of curves.

Ref the link above I have two questions:

1. Why does the original code not compile - is it because the type checker is run before the macro expansion?
2. If commenting out lines 72 & 73 -> why is the result not as expected? Surely the inner "x" should here shadow the outer one?

Thanks for any pointers

[alice]

The problem is macro hygiene which ensures that variables defined inside a macro are in a different namespace from variables outside the macro. Consider making the variable name an input to the macro?

For exapmle, try this

[vron]

Thanks,

Macro hygiene is a good key-word for me to explore furhter.

Indeed your example is a good way to work around it - thanks.

[jjpe]

@vron

is it because the type checker is run before the macro expansion?

Macro expansion happens before:

1. Type checking
2. Borrow checking

In fact, given the way it works, macro expansion is one of the earliest steps of the compilation process, probably right after parsing.