rust-unofficial/patterns

Incorrect text in Command pattern description

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#346 opened on Feb 18, 2023

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A-patternC-amendmentgood first issue

Description

Since function pointers implement all three traits Fn, FnMut, and FnOnce we could as well pass and store closures instead of function pointers.

This is not exactly correct function pointers can be created only from non-capturing closures. Which can be easily verified if you change example little bit:

error[[E0308]](https://doc.rust-lang.org/stable/error_codes/E0308.html): mismatched types
  --> src/main.rs:41:26
   |
41 |     schema.add_migration(|| format!("create {}",table), || "drop table".to_string());
   |            ------------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected fn pointer, found closure
   |            |
   |            arguments to this function are incorrect
   |
   = note: expected fn pointer `fn() -> String`
                 found closure `[closure@src/main.rs:41:26: 41:28]`
note: closures can only be coerced to `fn` types if they do not capture any variables

Contributor guide

Tech stack
rust
Domain
documentation
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
1
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic understanding of Rust closuresfunction pointers
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80
Research direction
Locate the Command pattern description in the repository's documentation. The incorrect text is in the section about function pointers. Correct the sentence to state that function pointers can be created from closures that do not capture any variables.