Julia中含感叹号的变量命名用法咨询

Hey there! Let's clear up the confusion around using exclamation marks (!) in Julia variable names, since it sounds like things worked initially in JuliaPro but got tricky after a restart.

First, let's get the basics straight: in Julia, the exclamation mark isn't a strict syntax rule—it's a community convention first and foremost. Here's how it's typically used:

• For functions: A ! at the end of a function name signals that the function mutates (modifies) one or more of its input arguments. Think push!() (adds to an array in-place) or sort!() (sorts an array without creating a new one). This is the most common use of ! in Julia code.
• For variables: While Julia's syntax does allow you to put ! in variable names (usually at the end), this is far less common. The convention here would be to use it for variables that represent mutable state—something you expect to modify repeatedly, like a buffer or a running counter.

Example of valid variable naming with ! #

You can define and use these variables just like any other, even after restarting JuliaPro:

# Define a variable with !
request_counter! = 0

# Modify it
request_counter! += 1

# Use it
println("Total requests: ", request_counter!)  # Outputs: Total requests: 1

Why you might have run into issues after restarting #

If things stopped working after a restart, here are a couple of common pitfalls to check:

1. Confusing variables with functions: If you tried to call your variable like a function (e.g., request_counter!()), Julia will throw an error—because it treats this as an attempt to run a function named request_counter!, not access the variable.
2. Name collisions with built-in functions: If you named your variable something like push! or sort!, you'd overwrite the built-in function. Later attempts to use that function (like push!([1], 2)) would fail because push! is now your variable, not the original function. Stick to unique names for your !-suffixed variables to avoid this.

A quick best practice note #

While variable names with ! are allowed, the Julia community mostly reserves ! for mutating functions. Unless your variable is explicitly representing mutable state that needs clear labeling, it's usually better to skip the ! to avoid confusion with function naming conventions.

内容的提问来源于stack exchange，提问作者lanselibai