Variables

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Summary

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• What is a variable?

• Declaration and definition

• Inside expressions

• Assignment operators

• Constants

• Extern variables

What is a variable?

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In programming, a variable could be defined like this: a memory space associated with an identifier, allocated statically or dynamically, whose lifetime depends on the programming language used.

Declaration and definition

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In Shard, variables (and other type of symbols) must be declared before being used. If a symbol is used but not declared, it does not exist from the point of view of the compiler. In Shard, the syntax used to declare a variable is the following:

// Declare
prefix name: type;

// Declare and define
prefix name: type = value;

Note: a variable declared without a value contains empty memory, not zeros. Using it could lead to an undefined behaviour (UB). Make sure to define all your variables.

For example:

var x: i32 = 42;

This line declares a variable named x of type i32 with a value of 42.

Inside expressions

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Identifiers can be used inside expressions. For example, you can try the following code, which adds two variables together (x and y) and store the result in z.

var x: i32 = 5;
var y: i32 = 4;
var z: i32 = x + y;

Now, z should have a value of 9 (5 + 4).

Assignment operators

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The value of a variable can be modified using assignment operators. The most common is =, which replaces the value of a variable by another, but there are other operators, which are mostly shortcuts:

x += 5;
// instead of
x = x + 5;

Here are all the assignment operators that can be used in Shard:

Operator	Effect
=	Sets x to y
+=	Sets x to x + y
-=	Sets x to x - y
*=	Sets x to x * y
/=	Sets x to x / y
%=	Sets x to x % y
&=	Sets x to x & y
|=	Sets x to x | y
^=	Sets x to x ^ y
~=	Sets x to ~y
<<=	Sets x to x << y
>>=	Sets x to x >> y

Constants

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If you do not want your variable to be modified, you can declare it as a constant, by using prefix const instead of var. Constants are read-only, so their value cannot be modified. This also means that assignment operators cannot be used on them.

const c: i32 = 5;
c *= 2;             // wrong

Extern variables

The extern keyword preceding a declaration or a function definitioncan be used to declare an extern symbol. You can use it like this:

// for a variable
extern var name: i32;
// for a function
extern func name(params) -> i32 {};

Note: DO NOT write in the body of extern functions or you will get an error from the C compiler.