There are six ways to pass parameters that cover all use cases, that can be written before the parameter name:

| Parameter ***kind*** | "Pass me an `x` I can ______" | Accepts arguments that are | Special semantics | ***kind*** `x: X` Compiles to Cpp1 as |

|---|---|---|---|---|

| `in` (default) | read from | anything | always `#!cpp const`<p>automatically passes by value if cheaply copyable | `X const x` or `X const& x` |

| `copy` | take a copy of | anything | acts like a normal local variable initialized with the argument | `X x` |

| `inout` | read from and write to | lvalues | | `X& x` |

| `out` | write to (including construct) | lvalues (including uninitialized) | must `=` assign/construct before other uses | `cpp2::impl::out<X>` |

| `move` | move from (consume the value of) | rvalues | automatically moves from every definite last use | `X&&` |

| `forward` | forward | anything | automatically forwards from every definite last use | `T&&` constrained to type `X` |

For example:

``` cpp title="Declaring parameters" hl_lines="2 3"

func: (

x : i32, // ('in' is default) x is const within func

inout y : std::string // y is modifiable

)

= {

// ...

}