Introduction

Attributes are metadata for the Wi compiler – an additional information that can alter how it behaves when dealing with certain variables. Syntax is simple:

name @attr := value;

Also can be used with function parameters:

f := |x @attr| => {
};

Now let's go over each one!

@const

Marks variable as read-only – any attempt to reassign it will cause a compile error

a @const := 10;
a = 20;

Will result in:

compile error: cannot reassign variable a
   |
 2 | a = 20;
   |   ^
   --> file.wi:2:3

@unused

Suppress unused local (or a function parameter) warning

f := |x| => {
};

compile warning: local variable x was defined but not used
   |
 1 | f := |x| => {
   |       ^
   --> file.wi:1:7

With @unused:

f := |x @unused| => {
};

(No warnings)

@deprecated

Mark variable as deprecated and warn on every use

x @deprecated := "hi";
std::puts(x);

compile warning: use of deprecated variable x
   |
 2 | std::puts(x);
   |           ^
   --> file.wi:2:11
hi

Combining

Attributes can be combined:

a @const @deprecated := 10;

Unknown attributes

An unknown attribute is a compile error:

compile error: unknown attribute hello
   |
 1 | a @hello := 0;
   |    ^^^^^
   --> file.wi:1:4

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