Data types

Last modified: 19 December 2024

DashaScript is a statically typed language. In general, the type system in DashaScript is similar to TypeScript's one, but it does not contain some of TS's elements (e. g. generics). Also, its syntax is slightly different.

Basic types

Table of built-in types:

Type name	Value range	Examples
string	string	“hello”, “123”, …
number	double-precision 64-bit binary format IEEE 754	5.2, -21, …
boolean	logical	true, false

You can declare the variable's type with a colon after its name. Any variable must have initial value (except for variable with nullable types).

Types can also be inferred during initialization, so you don't need to set it manually (see examples below).

Declaration of variables in the context:

context
{
    num: number = 0;
    str: string = "Hello";
    // flag's type will be infered to be boolean
    flag = false;
}

Declaration of local variables:

node some_node
{
    do
    {
        var num: number = 0;
        // str's type will be infered to be string
        var str = "Hello";
        var flag: boolean = false;
    }
}

string

The string type represents textual data. Any string literal value in code must be surrounded by double quotes (e.g. "Any string value").

Arithmetic operators:

Operator	Description	Return type	Example
`+`	concatenation of two strings	`string`	`"aba" + "caba" // "abacaba"`

Assignment operators:

Operator	Description	Example
`=`	direct assignment	`var s: string = "aba"; // s == "aba"`, `set s = "caba"; // s == "caba"`
`+=`	concatenation assignment	`var s: string = "aba";` `set s += "caba"; // s == "abacaba"`

Comparison operators:

Operator	Description	Return type	Example
`==`	check if two strings are equal	`boolean`	`"aba" == "aba" // true`
`!=`	check if two strings are not equal	`boolean`	`"aba" != "aba" // false`

string literal type

String literal type can be considered as special case of type string. A variable of string literal type may have only one value. For example: var s: "abacaba" = "abacaba".

You may use string literals to create constant/unmodifiable variables or to limit possible values of a variable (using string literals and unions)

Apart from the aspect described above, string literals act like simple strings.

number

The number type represents numeric data that can be expressed as a number. All basic arithmetic operations are supported.

Arithmetic operators:

Operator	Description	Return type	Example
`+`	addition of two numbers	`number`	`11 + 4 // 15`
`-`	subtraction of two numbers	`number`	`11 - 4 // 7`
`*`	multiplication of two numbers	`number`	`11 * 4 // 44`
`/`	division of two numbers	`number`	`11 / 4 // 2.75`
`%`	modulo (remainder) of two numbers	`number`	`11 % 4 // 2`

Assignment operators:

Operator	Description	Example
`=`	direct assignment	`var n: number = 11; // n == 11` `set n = 4 // n == 4`
`+=`	addition assignment	`var n: number = 11;` `set n += 4; // n == 15`
`-=`	subtraction assignment	`var n: number = 11;` `set n -= 4; // n == 7`

Comparison operators:

Operator	Description	Return type	Example
`==`	equal to	`boolean`	`6 == 4 // false`
`!=`	unequal to	`boolean`	`6 != 4 // true`
`<`	less than	`boolean`	`6 < 4 // false`
`<=`	less than or equal to	`boolean`	`6 <= 4 // false`
`>`	greater than	`boolean`	`6 > 4 // true`
`>=`	greater than or equal to	`boolean`	`6 >= 4 // true`

boolean

The boolean represents logical data type: true/false.

Logical operators:

Operator	Synonym	Description	Return type	Example
\|\|	`or`	logical or	`boolean`	`true` \|\| `false == true`
`&&`	`and`	logical and	`boolean`	`true and false == false`
`!`	---	logical negation	`boolean`	`!true == false`

Assignment operators:

Operator	Description	Example
`=`	direct assignment	`var b: boolean = true; // b == true` `set b = false; // b == false`

Comparison operators:

Operator	Description	Return type	Example
`==`	equal to	`boolean`	`true == true // true`
`!=`	unequal to	`boolean`	`true != true // false`

Nullable types

Nullable types allow the value to be set to the special value null instead of usual values of the data type.

A variable of nullable type may not have any initial value. In that case such a variable will have the value of null.

Use ? to declare type as nullable: var x: number?;.

null-checking

Most operations that are supported for non-nullable types are not supported for nullable types. For example, we can't concatenate values of type string and string? since second one can be null. That is why null-checking when working with nullable variables.

To check variable does not equal to null use the following syntax:

var checkIsNull: boolean = someVariable is not null;

And similarly when checking the variable has the value of null:

if (someVariable is null) { ... }

After a value is checked to be equal to null this information will be used later in corresponding context.

Example

context 
{
    someString: string?;
}

node some_node
{
    do 
    {
        if (someString is not null)
        {
            // someString is considered as not null in this block
            #sayText(someString);
        }
    }
}

Derived data types

Union types

You can create custom type that allows the variable to have values of several previously defined types (union of types).

Union of types may be enclosed in angle brackets (may be not), the combined types are separated by a pipe:

context
{
    status: <"none"|"done"> = "none";
    numberOrString: <number|string> = 0;
}

node some_node
{
    do
    {
        set status = "done";
        set numberOrString = "hello";
    }
}

Array

To declare array use the type of the elements followed by []: var arrayOfStrings: string[] = [];.

To access element of an array use []. The access result is a nullable value since provided index may occur to be out of array range.

Example

context
{
  arrayOfStrings: string[] = ["str1", "str2"];
}

node some_node
{
    do
    {
        var element = arrayOfStrings[0];
        if (element is not null)
        {
            // element is considered as string
        }
    }
}

Object

Object declaration is enclosed in curly braces, the object fields are declared as name and type, separated by a colon, each field declaration ends with a semicolon:

context
{
    // Declaration of an "person" object with field "name", field "age" and nullable field "phone".
    person: {
        name: string;
        age: number;
        phone: string?;
        role: <"student"|"professor">;
    } = {
        name: "Allen",
        age: 28,
        phone: null,
        role: "student"
    };
}

You can access field values of some object using the dot symbol:

node some_node
{
    do
    {
        #sayText("Person '" + $person.name + "', " + $person.sex + ", " + #stringify($person.age) + " years old");
    }
}

Other types

unknown

A variable of this type may contain any value that can be obtained in DashaScript:

    var u1: unknown = null;
    var u2: unknown = 1;
    var u3: unknown = "string";
    var u4: unknown = {flag: false, value: "value"};

There are no supported operations for this type.

empty

Special type that does not contain any values.

It can be used to denote that external function or block does not return any usable value.

The instance of this type can't be constructed explicitly. There are no supported operations for this type.

User-defined types

You can declare a custom type using the type keyword:

type MyType = {
    name: string; age: number;
};

It is better to declare your types before context section.

You may also create a special .dsl file with type declarations and include it in other .dsl files.

Example

type Role = <"student"|"professor">;
type Person = {
    name: string;
    age: number;
    phone: string?;
    role: Role;
};

context
{
    persons: Person[] = [{name: "Bob", age: 20, role: "student"}];
}

node some_node
{
    do
    {
        var firstPerson: string? = $persons[0];
        if (firstPerson is not null) {
            sayText("Hello, " + firstPerson.name + "! You are the first person.");
        } else {
            sayText("Array is empty.")
        }
    }
}

Type compatibility

DashaScript uses structural typing rules, similar to TypeScript. In short, that means that a value of type A can be assigned to a variable of type B only if A has all the properties of B, and the types of all of those are compatible with the types of properties of B. Here are several examples:

type A = {
    prop1: number;
    prop2: number;
};

// A is assignable to B
type B = {
    prop1: number;
};

// A is not assignable to C1: types of prop1 are not compatible
type C1 = {
    prop1: string;
};

// A is not assignable to C2: property prop3 is missing in A
type C2 = {
    prop3: number;
};

Type casting

You can convert between types using the as operator. It performs "deep" type checking, recursively checking of the properties of its operand. If successful, val as Type returns val converted to the type Type. If not, it returns null. Thus, the type of the expression val as Type is Type?.

These examples use types defined in the previous section:

var a = { prop1: 1, prop2: 2 };

var b = a as B;
// equivalent to
// var b: B? = { prop1: 1, prop2: 2 };

var c1 = a as C1;
// equivalent to
// var c1: C1? = null;

// use the result after a null check
if (b is not null) {
    // ...
}

// or use the optional access operators
#log(b?.prop1);

Found a mistake? Let us know.

Data types

Basic types

string

string literal type

number

boolean

Nullable types

null-checking

Example

Derived data types

Union types

Array

Example

Object

Other types

unknown

empty

User-defined types

Example

Type compatibility

Type casting

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