Is macro_rules a regular macro?

Question

I'm trying to understand rust macro syntax. Here I read that macro may be invoked generally in 3 flavours:

mymacro!(<tokens>);
mymacro![<tokens>];
mymacro!{<tokens>};

...and then I see an example macro definition also using macro (macro_rules), but the syntax doesn't conform to these rules:

macro_rules! name {<tokens>}

Is name a token and we have 4-th legal macro invocation form here or macro_rules is rather a keyword than just macro and uses special syntax not available for regular macros?

score 9 · Accepted Answer · answered Oct 06 '21 at 19:22

9

No, macro_rules is a special "directive". You can check the compiler syntax tree here. The important part is:

Syntax
MacroRulesDefinition :
   macro_rules ! IDENTIFIER MacroRulesDef

You can see that it is the entry point of the macros syntax.

answered Oct 06 '21 at 19:22

Netwave

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I don't know if directive is the correct word for this actually. So an edit is welcome to specify this. – Netwave Oct 06 '21 at 19:25
The term I've seen commonly used is "compiler built-in" – Ivan C Oct 06 '21 at 20:44

Is macro_rules a regular macro?

1 Answers1