Not clear sentence "Eager expansion generally performs a subset of the things that lazy (normal) expansion does." #1871
Labels
A-macros
Area: macros (general sense)
E-hard
Difficulty: might require advanced knowledge
I-confusing
Issue: info is confusing to readers
T-compiler
Relevant to compiler team
In https://rustc-dev-guide.rust-lang.org/macro-expansion.html I fear the sentence
is not clear. And I'd suggest, maybe, to give an example in order to clarify it.
I could imagine that you mean that, in the following example
an eager expansion would lead to a single expansion of
bar
while the normal expansion will lead to two expansions ofbar
.However, the query system that was described in the previous section seems to indicate that the expansion would consist in a single query call with a cached result, so that would be very cheap.
Also, if we consider
an eager expansion would lead to expending bar, while a normal expansion would avoid this expansion; showing that there are also case where the eager expansion do more work.
My best hypothesis, to be honest, right now, is that the sentence should be read with eager and lazy reversed
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