2.4. Expressions¶
2.4.1. Assignment¶
exp := exp '=' exp
exp := exp '<-' exp
exp := exp ':=' exp
Daslang implements 3 kind of assignment: copy assignment(=):
a = 10
Copy assignment is equivalent of C++ memcpy operation:
template <typename TT, typename QQ>
__forceinline void das_copy ( TT & a, const QQ b ) {
static_assert(sizeof(TT)<=sizeof(QQ),"can't copy from smaller type");
memcpy(&a, &b, sizeof(TT));
}
“Move” assignment:
var b = new Foo
var a: Foo?
a <- b
Move assignment nullifies source (b). It’s main purpose is to correctly move ownership, and optimize copying if you don’t need source for heavy types (such as arrays, tables). Some external handled types can be non assignable, but still moveable.
Move assignment is equivalent of C++ memcpy + memset operations:
template <typename TT, typename QQ>
__forceinline void das_move ( TT & a, const QQ & b ) {
static_assert(sizeof(TT)<=sizeof(QQ),"can't move from smaller type");
memcpy(&a, &b, sizeof(TT));
memset((TT *)&b, 0, sizeof(TT));
}
“Clone” assignment:
a := b
Clone assignment is syntactic sugar for calling clone(var a: auto&; b: auto&) if it exists or basic assignment for POD types. It is also implemented for das_string, array and table types, and creates a ‘deep’ copy.
Some external handled types can be non assignable, but still cloneable (see Clone).
2.4.2. Operators¶
2.4.2.1. .. Operator¶
expr1 \.\. expr2
This is equivalent to interval(expr1,expr2). By default interval(a,b:int) is implemented as range(a,b), and interval(a,b:uint) is implemented as urange(a,b). Users can define their own interval functions or generics.
2.4.2.2. ?: Operator¶
exp := exp_cond '?' exp1 ':' exp2
This conditionally evaluate an expression depending on the result of an expression. If expr_cond is true, only exp1 will be evaluated. Similarly, if false, only exp2.
2.4.2.3. ?? Null-coalescing operator¶
exp := exp1 '??' exp2
Conditionally evaluate exp2 depending on the result of exp1. The given code is equivalent to:
exp := (exp1 '!=' null) '?' *exp1 ':' exp2
It evaluates expressions until the first non-null value (just like | operators for the first ‘true’ one).
Operator precedence is also follows C# design, so that ?? has lower priority than |
2.4.2.4. ?. and ?[ - Null-propagation operator¶
exp := value '?.' key
If the value is not null, then dereferences the field ‘key’ for struct, otherwise returns null.
struct TestObjectFooNative
fooData : int
struct TestObjectBarNative
fooPtr: TestObjectFooNative?
barData: float
def test
var a: TestObjectFooNative?
var b: TestObjectBarNative?
var idummy: int
var fdummy: float
a?.fooData ?? idummy = 1 // will return reference to idummy, since a is null
assert(idummy == 1)
a = new TestObjectFooNative
a?.fooData ?? idummy = 2 // will return reference to a.fooData, since a is now not null
assert(a.fooData == 2 & idummy == 1)
b = new TestObjectBarNative
b?.fooPtr?.fooData ?? idummy = 3 // will return reference to idummy, since while b is not null, but b.?barData is still null
assert(idummy == 3)
b.fooPtr <- a
b?.fooPtr?.fooData ?? idummy = 4 // will return reference to b.fooPtr.fooData
assert(b.fooPtr.fooData == 4 & idummy == 3)
Additionally, null propagation of index ?[ can be used with tables:
var tab <- {{ "one"=>1; "two"=> 2 }}
let i = tab?["three"] ?? 3
print("i = {i}\n")
It checks both the container pointer and the availability of the key.
2.4.2.5. Arithmetic¶
exp:= 'exp' op 'exp'
Daslang supports the standard arithmetic operators +, -, *, / and %.
It also supports compact operators +=, -=, *=, /=, %= and
increment and decrement operators ++ and --:
a += 2
// is the same as writing
a = a + 2
x++
// is the same as writing
x = x + 1
All operators are defined for numeric and vector types, i.e (u)int* and float* and double.
2.4.2.6. Relational¶
exp:= 'exp' op 'exp'
Relational operators in Daslang are : ==, <, <=, >, >=, !=.
These operators return true if the expression is false and a value different than true if the expression is true.
2.4.2.7. Logical¶
exp := exp op exp
exp := '!' exp
Logical operators in Daslang are : &&, ||, ^^, !, &&=, ||=, ^^=.
The operator && (logical and) returns false if its first argument is false, or otherwise returns
its second argument.
The operator || (logical or) returns its first argument if is different than false, or otherwise
returns the second argument.
The operator ^^ (logical exclusive or) returns true if arguments are different, and false otherwise.
It is important to understand, that && and || will not necessarily ‘evaluate’ all their arguments. Unlike their C++ equivalents, &&= and ||= will also cancel evaluation of the right side.
The ‘!’ (negation) operator will return false if the given value was true, or false otherwise.
2.4.2.8. Bitwise Operators¶
exp:= 'exp' op 'exp'
exp := '~' exp
Daslang supports the standard C-like bitwise operators &, |, ^, ~, <<, >>, <<<, >>>.
Those operators only work on integer values.
2.4.2.9. Pipe Operators¶
exp:= 'exp' |> 'exp'
exp:= 'exp' <| 'exp'
Daslang supports pipe operators. Pipe operators are similar to ‘call’ expressions where the other expression is first argument.
def addX(a, b)
assert(b == 2 || b == 3)
return a + b
def test
let t = 12 |> addX(2) |> addX(3)
assert(t == 17)
return true
def addOne(a)
return a + 1
def test
let t = addOne() <| 2
assert(t == 3)
The lpipe macro allows piping to the previous line:
require daslib/lpipe
def main
print()
lpipe() <| "this is string constant"
In the example above, the string constant will be piped to the print expression on the previous line. This allows piping of multiple blocks while still using significant whitespace syntax.
2.4.2.10. Operators precedence¶
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2.4.3. Array Initializer¶
exp := '[['type[] [explist] ']]'
Creates a new fixed size array:
let a = [[int[] 1; 2]] // creates array of two elements
let a = [[int[2] 1; 2]] // creates array of two elements
var a = [[auto 1; 2]] // creates which fully infers its own type
let a = [[int[2] 1; 2; 3]] // error, too many initializers
var a = [[auto 1]] // int
var a = [[auto[] 1]] // int[1]
Arrays can be also created with array comprehensions:
let q <- [[ for x in range(0, 10); x * x ]]
Similar syntax can be used to initialize dynamic arrays:
let a <- [{int[3] 1;2;3 }] // creates and initializes array<int>
let q <- [{ for x in range(0, 10); x * x }] // comprehension which initializes array<int>
Only dynamic multi-dimensional arrays can be initialized (for now):
var a <- [[auto [{int 1;2;3}]; [{int 4;5}]]] // array<int>[2]
var a <- [{auto [{int 1;2;3}]; [{int 4;5}]}] // array<array<int>>
(see Arrays, Comprehensions).
2.4.4. Struct, Class, and Handled Type Initializer¶
struct Foo
x: int = 1
y: int = 2
let fExplicit = [[Foo x = 13, y = 11]] // x = 13, y = 11
let fPartial = [[Foo x = 13]] // x = 13, y = 0
let fComplete = [[Foo() x = 13]] // x = 13, y = 2 with 'construct' syntax
let aArray = [[Foo() x=11,y=22; x=33; y=44]] // array of Foo with 'construct' syntax
Initialization also supports optional inline block:
var c = [[ Foo x=1, y=2 where $ ( var foo ) { print("{foo}"); } ]]
Classes and handled (external) types can also be initialized using structure initialization syntax. Classes and handled types always require constructor syntax, i.e. ().
2.4.5. Tuple Initializer¶
Create new tuple:
let a = [[tuple<int;float;string> 1, 2.0, "3"]] // creates typed tuple
let b = [[auto 1, 2.0, "3"]] // infers tuple type
let c = [[auto 1, 2.0, "3"; 2, 3.0, "4"]] // creates array of tuples
(see Tuples).
2.4.6. Variant Initializer¶
Variants are created with a syntax similar to that of a structure:
variant Foo
i : int
f : float
let x = [[Foo i = 3]]
let y = [[Foo f = 4.0]]
let a = [[Foo[2] i=3; f=4.0]] // array of variants
let z = [[Foo i = 3, f = 4.0]] // syntax error, only one initializer
(see Variants).