Update 'practical macros' section to use '=>' instead of '...' syntax… #107
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… in the provided examples. This hopefully alleviates confusion that can stem from using the current example code and seeing errors related to the tokens instead of an expected error related to unimplemented code
Veykril
reviewed
Aug 23, 2024
| @@ -32,20 +32,23 @@ So, with all that having been said, let's get started. | |||
| ## Construction | |||
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| Usually, when working on a new `macro_rules!` macro, the first thing I do is decide what the invocation should look like. | |||
| In this specific case, my first attempt looked like this: | |||
| In this specific case, my second* attempt looked like this: | |||
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This is rather confusing wording, makes the reader question about the first attempt
Comment on lines
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| # if self.pos < 2 { | ||
| # let next_val = self.mem[self.pos]; | ||
| # self.pos += 1; | ||
| # Some(next_val) | ||
| # } else { | ||
| # let next_val = { | ||
| # let n = self.pos; | ||
| # let a = IndexOffset { slice: &self.mem, offset: n }; | ||
| # (a[n-2] + a[n-1]) | ||
| # }; | ||
| # | ||
| # { | ||
| # use std::mem::swap; | ||
| # | ||
| # let mut swap_tmp = next_val; | ||
| # for i in (0..2).rev() { | ||
| # swap(&mut swap_tmp, &mut self.mem[i]); | ||
| # } | ||
| # } | ||
| # | ||
| # self.pos += 1; | ||
| # Some(next_val) | ||
| # } | ||
| if self.pos < 2 { | ||
| let next_val = self.mem[self.pos]; | ||
| self.pos += 1; | ||
| Some(next_val) | ||
| } else { | ||
| let next_val = { | ||
| let n = self.pos; | ||
| let a = IndexOffset { slice: &self.mem, offset: n }; | ||
| (a[n-2] + a[n-1]) | ||
| }; | ||
| { | ||
| use std::mem::swap; | ||
| let mut swap_tmp = next_val; | ||
| for i in (0..2).rev() { | ||
| swap(&mut swap_tmp, &mut self.mem[i]); | ||
| } | ||
| } | ||
| self.pos += 1; | ||
| Some(next_val) | ||
| } |
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This is intentionally hidden, its noise regarding the change described
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Edited this chapter slightly to ensure as much code as possible is valid throughout or where it is not, ensure that any errors are 'obvious' and not distracting of the chapters intent. Specifically, I updated the example code to use
=>instead of...in the macro pattern match. The later value is not actually usable without additional delimiters and results in misleading errors in code that references the macro. This can lead a reader to think they don't correctly understand the parsing structure and clarification doesn't happen until much later in the chapter, rendering all of the previous code examples effectively unusable if they're (likely) following along.