2.5. Expressions

2.5.1. Assignment

exp := derefexp '=' exp
exp:= derefexp '<-' exp

squirrel implements 2 kind of assignment: the normal assignment(=):

a = 10;

and the “new slot” assignment.:

a <- 10;

The new slot expression allows to add a new slot into a table(see Tables). If the slot already exists in the table it behaves like a normal assignment.

2.5.2. Operators ?: Operator

exp := exp_cond '?' exp1 ':' exp2

conditionally evaluate an expression depending on the result of an expression. Arithmetic

exp:= 'exp' op 'exp'

Squirrel supports the standard arithmetic operators +, -, *, / and %. Other than that is also supports compact operators (+=,-=,*=,/=,%=) and increment and decrement operators(++ and –);:

a += 2;
//is the same as writing
a = a + 2;
//is the same as writing
x = x + 1

All operators work normally with integers and floats; if one operand is an integer and one is a float the result of the expression will be float. The + operator has a special behavior with strings; if one of the operands is a string the operator + will try to convert the other operand to string as well and concatenate both together. For instances and tables, _tostring is invoked. Relational

exp:= 'exp' op 'exp'

Relational operators in Squirrel are : ==, <, <=, <, <=, !=

These operators return true if the expression is false and a value different than true if the expression is true. Internally the VM uses the integer 1 as true but this could change in the future. 3 ways compare

exp:= 'exp' <=> 'exp'

the 3 ways compare operator <=> compares 2 values A and B and returns an integer less than 0 if A < B, 0 if A == B and an integer greater than 0 if A > B. Logical

exp := exp op exp
exp := '!' exp

Logical operators in Squirrel are : &&, ||, !

The operator && (logical and) returns null if its first argument is null, otherwise returns its second argument. The operator || (logical or) returns its first argument if is different than null, otherwise returns the second argument.

The ‘!’ operator will return null if the given value to negate was different than null, or a value different than null if the given value was null. in operator

exp:= keyexp 'in' tableexp

Tests the existence of a slot in a table. Returns true if keyexp is a valid key in tableexp

local t=
    foo="I'm foo",
    [123]="I'm not foo"

if("foo" in t) dostuff("yep");
if(123 in t) dostuff(); instanceof operator

exp:= instanceexp 'instanceof' classexp

Tests if a class instance is an instance of a certain class. Returns true if instanceexp is an instance of classexp. typeof operator

exp:= 'typeof' exp

returns the type name of a value as string.:

local a={},b="squirrel"
print(typeof a); //will print "table"
print(typeof b); //will print "string" Comma operator

exp:= exp ',' exp

The comma operator evaluates two expression left to right, the result of the operator is the result of the expression on the right; the result of the left expression is discarded.:

local j=0,k=0;
for(local i=0; i<10; i++ , j++)
    k = i + j;
local a,k;
a = (k=1,k+2); //a becomes 3 Bitwise Operators

exp:= 'exp' op 'exp'
exp := '~' exp

Squirrel supports the standard c-like bit wise operators &, |, ^, ~, <<, >> plus the unsigned right shift operator <<<. The unsigned right shift works exactly like the normal right shift operator(<<) except for treating the left operand as an unsigned integer, so is not affected by the sign. Those operators only work on integers values, passing of any other operand type to these operators will cause an exception. Operators precedence

-, ~, !, typeof , ++, -- highest
/, *, % ...
+, -  
<<, >>, >>>  
<, <=, >, >=  
==, !=, <=>  
&&, in  
+=, =, -= ...
,(comma operator) lowest

2.5.3. Table Constructor

tslots := ( 'id' '=' exp | '[' exp ']' '=' exp ) [',']
exp := '{' [tslots] '}'

Creates a new table.:

local a = {} //create an empty table

A table constructor can also contain slots declaration; With the syntax:

local a = {
    slot1 = "I'm the slot value"

An alternative syntax can be:

'[' exp1 ']' = exp2 [',']

A new slot with exp1 as key and exp2 as value is created:

local a=
    [1]="I'm the value"

both syntaxes can be mixed:

local table=
    function bau(a,b)
        return a+b;

The comma between slots is optional. Table with JSON syntax

Since Squirrel 3.0 is possible to declare a table using JSON syntax(see http://www.wikipedia.org/wiki/JSON).

the following JSON snippet:

local x = {
  "id": 1,
  "name": "Foo",
  "price": 123,
  "tags": ["Bar","Eek"]

is equivalent to the following squirrel code:

local x = {
  id = 1,
  name = "Foo",
  price = 123,
  tags = ["Bar","Eek"]

2.5.4. clone

exp:= 'clone' exp

Clone performs shallow copy of a table, array or class instance (copies all slots in the new object without recursion). If the source table has a delegate, the same delegate will be assigned as delegate (not copied) to the new table (see Delegation).

After the new object is ready the “_cloned” meta method is called (see Metamethods).

When a class instance is cloned the constructor is not invoked(initializations must rely on `_cloned` instead

2.5.5. Array contructor

exp := '[' [explist] ']'

Creates a new array.:

a <- [] //creates an empty array

arrays can be initialized with values during the construction:

a <- [1,"string!",[],{}] //creates an array with 4 elements