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author魏曹先生 <1992414357@qq.com>2026-07-10 16:23:18 +0800
committer魏曹先生 <1992414357@qq.com>2026-07-10 16:26:13 +0800
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parent73d0f0185f94a8733dfb5eb538298447ab8977b3 (diff)
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-# Remove `r_print!` and `r_println!` Macros
-
-`r_print!` and `r_println!` are important macros in Mingling for use inside `#[help]` and `#[renderer]` functions, but their implementation is not clean: they implicitly introduce a `__renderer_inner_result` field. While this might look elegant at the API level, it is **incorrect** and even **objectionable**.
-
-## Why **Objectionable**?
-
-Because you can't define declarative macros with `macro_rules` that wrap them.
-
-This is because `r_println!` depends on the implicit variable `__renderer_inner_result` injected by the `#[renderer]` proc macro into the function body. However, when a `macro_rules` declarative macro expands, **its internal code is placed in the caller's context**, which does not contain `__renderer_inner_result` — that variable only exists within the direct scope of the function body processed by `#[renderer]`.
-
-Let's look at some code to see why:
-
-```rust
-// Suppose you want to write a wrapper macro:
-macro_rules! my_println {
- ($($arg:tt)*) => {
- // When expanded here, the context is the call site of my_println!,
- // not the location where the renderer function's injected variables live.
- // So __renderer_inner_result is NOT visible here!
- r_println!("Custom: {}", format!($($arg)*));
- };
-}
-
-#[renderer]
-fn render_something(_p: ResultSomething) {
- // Although this function body has __renderer_inner_result injected,
- // the code from my_println! does NOT expand "inside this function body" —
- // macro_rules expansion is essentially text replacement. The replaced code
- // lives at the line where my_println! is called, and any variables referenced
- // inside that macro must resolve to identifiers accessible at the call site.
- // __renderer_inner_result is not a public, path-accessible variable;
- // it's a hygienic local variable generated by the `#[renderer]` macro,
- // and external macros cannot directly access it by name.
- my_println!("{}", box_val); // Compile error: cannot find __renderer_inner_result
-}
-```
-
-## Deeper Issues
-
-I have to admit, this is an early design flaw. After re-examining the code, I found the problem goes beyond "can't be wrapped".
-
-This isn't just a "can't wrap" issue — it reflects that `r_println!`'s design fundamentally violates Rust's macro hygiene principles:
-
-- **Implicit dependency**: Users of the macro must know that a variable named `__renderer_inner_result` exists — but this variable is neither part of the public API nor explicitly documented anywhere.
-- **Scope leakage**: Variables injected by a proc macro should be confined to the scope processed by that macro. But `r_println!` attempts to make that variable accessible across macro calls, which effectively breaks Rust's identifier hygiene.
-- **Non-composable**: Any attempt to wrap `r_println!` will fail, because declarative macros cannot "pass through" access to implicit variables. Even using a proc macro to wrap it would encounter similar hygiene issues.
-
-## Desired New Syntax
-
-I've designed two alternative approaches and will choose based on actual needs.
-
-### Option 1: Explicit Return
-
-```rust
-#[renderer]
-fn render_something(prev: ResultSomething) -> RenderResult {
- let mut result = RenderResult::new();
- result.println(prev.to_string());
- // or
- write!(result, "{}", prev.to_string());
-
- result // return here
-}
-```
-
-Clear boundaries — the entire rendering process is confined within the function body decorated by `#[help]` or `#[renderer]`, without introducing extra out-of-scope dependencies. The trade-off is slightly more boilerplate compared to the original approach.
-
-### Option 2: Resource Injection
-
-```rust
-#[renderer]
-fn render_something(prev: ResultSomething, result: &mut ResRenderResult) {
- result.println(prev.to_string());
- // or
- write!(result, "{}", prev.to_string());
-
- result // return here
-}
-```
-
-More flexible, but blurs the boundary between logic functions like `#[chain]` and rendering functions like `#[help]`.
-
-### Preferred Direction
-
-I lean toward **Option 1 (Explicit Return)**. There's no need to turn `RenderResult` into `ResRenderResult` as a global resource.
-
-As for rendering in logic functions like `#[chain]`, that should be handled by a separate system — not discussed here.