Restore Writer.write_char, see #10861. #11310
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…=xFrednet,djc [`slow_vector_initialization`]: clarify why `Vec::new()` + resize is worse rust-lang#11198 extended this lint to also warn on `Vec::new()` + `resize(0, len)`, but did not update the lint documentation, so it left some confused (rust-lang/rust-clippy#10938 (comment)). This PR should make it a bit more clear. (cc `@djc` `@vi` what do you think about this?) <details> <summary>More details</summary> Godbolt for `Vec::new()` + `.resize(x, 0)`: https://godbolt.org/z/e7q9xc9rG The resize call first does a normal allocation (`__rust_alloc`): ```asm alloc::raw_vec::finish_grow: ... cmp qword ptr [rcx + 8], 0 je .LBB1_7 ; if capacity == 0 -> LBB1_7 .LBB1_7: ... call qword ptr [rip + __rust_alloc@GOTPCREL] ``` *Then* a memset for zero initialization: ```asm example::f: ... xor esi, esi ; 0 call qword ptr [rip + memset@GOTPCREL] ``` ------------ Godbolt for `vec![0; len]`: https://godbolt.org/z/M3vr53vWY Important bit: ```asm example::f: ... call qword ptr [rip + __rust_alloc_zeroed@GOTPCREL] ``` </details> changelog: [`slow_vector_initialization`]: clarify why `Vec::new()` + resize is worse than `vec![0; len]`
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