参数与实参
编译时值与运行时值
参数与实参 是 CoddyKit 上的免费 Mojo Academy 课时。 这是第 1 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Mojo Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Mojo Academy 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
Two Kinds of Input
Mojo functions can take two kinds of input: parameters known at compile time, and arguments known at runtime. Knowing the difference is the key.
Arguments Live at Runtime
An argument is an ordinary value you pass when the program runs. Its actual number can change every single time you call the function.
fn square(x: Int) -> Int:
return x * xParameters Live at Compile Time
A parameter is a value the compiler already knows before your program runs. It is fixed and baked right into the generated code. ⚙️
Brackets vs Parentheses
Mojo keeps them visually separate: parameters go in square brackets, while arguments stay in the familiar parentheses.
fn repeat[count: Int](msg: String):
print(msg)Reading the Signature
In repeat[count: Int](msg: String), the count is set at compile time and msg is supplied later when you actually call it.
Compile Time Means Earlier
Think of compile time as the moment Mojo translates your code, long before it runs. Parameters are decided in that earlier phase.
Why Separate Them
Keeping compile-time and runtime values separate lets the compiler specialize and optimize code that the runtime simply cannot.
Passing a Parameter
You supply a parameter in brackets at the call site, just like you supply arguments in parentheses right after it.
repeat[3]("hi")Parameters Must Be Known
A parameter value must be a compile-time constant. You cannot pass a number you only computed while the program was running.
A Familiar Example
The built-in SIMD type takes its element type and width as parameters, then holds real numbers as runtime values inside it.
var v = SIMD[DType.int32, 4](1, 2, 3, 4)The Mental Model
Picture two slots: the bracket slot for compile-time facts, the parenthesis slot for runtime data. Mojo treats them very differently.
Quick Check
Tell apart parameters and arguments in Mojo.
Recap
You learned the split: parameters are compile-time values in brackets, arguments are runtime values in parentheses. That divide powers Mojo's speed. 🎯
常见问题解答
「参数与实参」课时是免费的吗？
是的 — 「参数与实参」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Mojo Academy 课程的其余内容，请升级到 CoddyKit PRO。 Mojo Academy 课程共包含 4 节课。
「参数与实参」这节课中我会学到什么？
编译时值与运行时值 你通过在浏览器中直接运行的动手代码来练习 Mojo Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Mojo Academy 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Mojo Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 1 节课，共 4 节。
「参数与实参」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Mojo Academy 课中编写并运行代码吗？
能。每节 Mojo Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。