Functions for working with data types

In addition to the ordinary functions that work with particular values (FIND, COALESCE types), YQL supports functions for working with types.
The functions enable you to find out the type of an arbitrary expression, analyze a container type, and create a new container type based on the existing one.

Examples

$itemType = TypeOf($item);
SELECT CAST($foo AS ListType($itemType));  -- cast $foo to type List<$itemType>

FormatType

Signature

FormatType(Type)->String

Serialization of a type or a type handle into a human-readable string. This is useful for debugging and will also be used in the following examples in this section. Format documentation.

ParseType

Signature

ParseType(String)->Type

Building a type by a string with its description. Its format documentation.

Examples

SELECT FormatType(ParseType("List<Int32>"));  -- List<int32>

TypeOf

Signature

TypeOf(<any expression>)->Type

Getting the value type passed to the argument.

Examples

SELECT FormatType(TypeOf("foo"));  -- String

SELECT FormatType(TypeOf(AsTuple(1, 1u))); -- Tuple<Int32,Uint32>

InstanceOf

Signature

InstanceOf(Type)->Type object

Returns an instance of the object of the specified type. The resulting object does not have any particular meaning.
InstanceOf can only be used if the result of the expression in which InstanceOf is used depends on the InstanceOf type, but not on the value.
Otherwise, the operation will be completed with an error.

Examples

SELECT InstanceOf(ParseType("Int32")) + 1.0; -- error (Can't execute InstanceOf): the result depends on the (undefined) value of InstanceOf
SELECT FormatType(TypeOf(
    InstanceOf(ParseType("Int32")) +
    InstanceOf(ParseType("Double"))
)); -- will return Double, because adding Int32 and Double returns Double (InstanceOf is used in the context where only its type is important, but not its value)

DataType

Signature

DataType(String, [String, ...])->Type

Returns the type for primitive data types by its name.
For some types (for example, Decimal), you need to pass type parameters as additional arguments.

Examples

SELECT FormatType(DataType("Bool")); -- Bool
SELECT FormatType(DataType("Decimal","5","1")); -- Decimal(5,1)

OptionalType

Signature

OptionalType(Type)->optional Type

Adds the ability to contain NULL to the passed type.

Examples

SELECT FormatType(OptionalType(DataType("Bool"))); -- Bool?
SELECT FormatType(OptionalType(ParseType("List<String?>"))); -- List<String?>?

ListType and StreamType

Signature

ListType(Type)->list type with items of the Type type
StreamType(Type)->stream type with items of the Type type

Builds a list or stream type based on the passed item type.

Examples

SELECT FormatType(ListType(DataType("Bool"))); -- List<Bool>

DictType

Signature

DictType(Type, Type)->dict type

Builds a dict type based on the passed key (first argument) and value (second argument) types.

Examples

SELECT FormatType(DictType(
    DataType("String"),
    DataType("Double")
)); -- Dict<String,Double>

TupleType

Signature

TupleType(Type, ...)->tuple type

Builds a tuple type based on the passed item types.

Examples

SELECT FormatType(TupleType(
    DataType("String"),
    DataType("Double"),
    OptionalType(DataType("Bool"))
)); -- Tuple<String,Double,Bool?>

StructType

Signature

StructType(Type AS ElementName1, Type AS ElementName2, ...)->structure type

Builds a structure type based on the passed item types. The standard syntax for named arguments is used to specify item names.

Examples

SELECT FormatType(StructType(
    DataType("Bool") AS MyBool,
    ListType(DataType("String")) AS StringList
)); -- Struct<'MyBool':Bool,'StringList':List<String>>

VariantType

Signature

VariantType(StructType)->variant type on top of structure
VariantType(TupleType)->variant type on top of tuple

Returns the variant type by the underlying type (structure or tuple).

Examples

SELECT FormatType(VariantType(
  ParseType("Struct<foo:Int32,bar:Double>")
)); -- Variant<'bar':Double,'foo':Int32>

ResourceType

Signature

ResourceType(String)->resource type

Returns the resource type by the passed string label.

Examples

SELECT FormatType(ResourceType("Foo")); -- Resource<'Foo'>

CallableType

Signature

CallableType(Uint32, Type, [Type, ...])->callable value type

Builds the callable value type based on the following arguments:

  1. Number of optional arguments (if all are mandatory, then 0).
  2. Result type.
  3. All subsequent CallableType arguments are interpreted as the argument types of the callable value with a shift of two mandatory ones (for example, the third CallableType argument describes the type of the first argument of the callable value).

Examples

SELECT FormatType(CallableType(
  1, -- optional args count
  DataType("Double"), -- result type
  DataType("String"), -- arg #1 type
  OptionalType(DataType("Int64")) -- arg #2 type
)); -- Callable<(String,[Int64?])->Double>

GenericType, UnitType and VoidType

Signature

GenericType()->type
UnitType()->type
VoidType()->type

Return special data types with the same name. There are no arguments, because they are not parameterized.

Examples

SELECT FormatType(VoidType()); -- Void

OptionalItemType, ListItemType and StreamItemType

Signature

OptionalItemType(OptionalType)->optional item type
ListItemType(ListType)->list item type
StreamItemType(StreamType)->stream item type

If a type is passed to these functions, they perform the action opposite to OptionalType, ListType, and StreamType — they return the item type by the type of the corresponding container.
If a type handle is passed to these functions, they perform the action opposite to OptionalTypeHandle, ListTypeHandle, and StreamTypeHandle — they return the item type handle by the type handle of the corresponding container.

Examples

SELECT FormatType(ListItemType(
  ParseType("List<Int32>")
)); -- Int32

SELECT FormatType(ListItemType(
  ParseTypeHandle("List<Int32>")
)); -- Int32

DictKeyType and DictPayloadType

Signature

DictKetType(DictType)->dict key type
DictPayloadType(DictType)->dict meaning type

Return the key or meaning type by the dict type.

Examples

SELECT FormatType(DictKeyType(
  ParseType("Dict<Int32,String>")
)); -- Int32

TupleElementType

Signature

TupleElementType(TupleType, String)->tuple item type

Returns the tuple item type by the tuple type and item index (index from zero).

Examples

SELECT FormatType(TupleElementType(
  ParseType("Tuple<Int32,Double>"), "1"
)); -- Double

StructMemberType

Signature

StructMemberType(StructType, String)->structure item type

Returns the structure item type by the structure type and item name.

Examples

SELECT FormatType(StructMemberType(
  ParseType("Struct<foo:Int32,bar:Double>"), "foo"
)); -- Int32

CallableResultType and CallableArgumentType

Signature

CallableResultType(CallableType)->callable value result type
CallableArgumentType(CallableType, Uint32)->callable value argument type

CallableResultType returns the result type by the callable value type and CallableArgumentType returns the argument type by the callable value type and its index (index from zero).

Examples

$callable_type = ParseType("(String,Bool)->Double");

SELECT FormatType(CallableResultType(
    $callable_type
)), -- Double
FormatType(CallableArgumentType(
    $callable_type, 1
)); -- Bool

VariantUnderlyingType

Signature

VariantUnderlyingType(VariantType)->underlying variant type

If a type is passed to this function, it performs the action opposite to VariantType — it returns the underlying type by the variant type.
If a type handle is passed to this function, it performs the action opposite to VariantTypeHandle — it returns the underlying type handle by the variant type handle.

Examples

SELECT FormatType(VariantUnderlyingType(
  ParseType("Variant<foo:Int32,bar:Double>")
)), -- Struct<'bar':Double,'foo':Int32>
FormatType(VariantUnderlyingType(
  ParseType("Variant<Int32,Double>")
)); -- Tuple<Int32,Double>

SELECT FormatType(VariantUnderlyingType(
  ParseTypeHandle("Variant<foo:Int32,bar:Double>")
)), -- Struct<'bar':Double,'foo':Int32>
FormatType(VariantUnderlyingType(
  ParseTypeHandle("Variant<Int32,Double>")
)); -- Tuple<Int32,Double>

Functions for working with data types during computations

To work with data types during computations, the type handle mechanism is used — the resource containing an opaque type description. After constructing a type handle, you can return to a regular type using the EvaluateType function. For debugging, convert the type handle into a string using the FormatType function.

TypeHandle

Getting a type handle from the type passed to the argument.

Signature

TypeHandle(Type)->хэндл типа

Examples:

SELECT FormatType(TypeHandle(TypeOf("foo")));  -- String

EvaluateType

Signature

EvaluateType(TypeHandle)->type

Getting a type from the type handle passed to the argument. The function is computed before the main computation process starts, just like EvaluateExpr.

Examples:

SELECT FormatType(EvaluateType(TypeHandle(TypeOf("foo"))));  -- String

ParseTypeHandle

Signature

ParseTypeHandle(String)->type handle

Building a type handle by a string with its description. Its format documentation.

Examples:

SELECT FormatType(ParseTypeHandle("List<Int32>"));  -- List<int32>

TypeKind

Signature

TypeKind(TypeHandle)->String

Getting the name of the top-level type from the type handle passed to the argument.

Examples:

SELECT TypeKind(TypeHandle(TypeOf("foo")));  -- Data
SELECT TypeKind(ParseTypeHandle("List<Int32>"));  -- List

DataTypeComponents

Signature

DataTypeComponents(DataTypeHandle)->List<String>

Getting the name and parameters of the primitive data type from the handle of the primitive type passed to the argument. The reverse function is DataTypeHandle.

Examples:

SELECT DataTypeComponents(TypeHandle(TypeOf("foo")));  -- ["String"]
SELECT DataTypeComponents(ParseTypeHandle("Decimal(4,1)"));  -- ["Decimal", "4", "1"]

DataTypeHandle

Signature

DataTypeHandle(List<String>)->handle of the primitive data type

Building a handle of the primitive data type from its name and parameters passed to the argument as a list. The reverse function is DataTypeComponents.

Examples:

SELECT FormatType(DataTypeHandle(
    AsList("String")
)); -- String

SELECT FormatType(DataTypeHandle(
    AsList("Decimal", "4", "1")
)); -- Decimal(4,1)

OptionalTypeHandle

Signature

OptionalTypeHandle(TypeHandle)->optional type handle

Adds the ability to contain NULL to the passed type handle.

Examples:

SELECT FormatType(OptionalTypeHandle(
    TypeHandle(DataType("Bool"))
)); -- Bool?

ListTypeHandle and StreamTypeHandle

Signature

ListTypeHandle(TypeHandle)->list type handle
StreamTypeHandle(TypeHandle)->stream type handle

Builds a list or stream type handle based on the passed item type handle.

Examples:

SELECT FormatType(ListTypeHandle(
    TypeHandle(DataType("Bool"))
)); -- List<Bool>

EmptyListTypeHandle and EmptyDictTypeHandle

Signature

EmptyListTypeHandle()->empty list type handle
EmptyDictTypeHandle()->empty dict type handle

Builds an empty list or dict type handle.

Examples:

SELECT FormatType(EmptyListTypeHandle()); -- EmptyList

TupleTypeComponents

Signature

TupleTypeComponents(TupleTypeHandle)->List<TypeHandle>

Getting the item type handle list from the tuple type handle passed to the argument. The reverse function is TupleTypeHandle.

Examples:

SELECT ListMap(
   TupleTypeComponents(
       ParseTypeHandle("Tuple<Int32, String>")
   ),
   ($x)->{
       return FormatType($x)
   }
); -- ["Int32", "String"]

TupleTypeHandle

Signature

TupleTypeHandle(List<TypeHandle>)->tuple type handle

Building a tuple type handle from the item type handles passed to the argument as a list. The reverse function is TupleTypeComponents.

Examples:

SELECT FormatType(
    TupleTypeHandle(
        AsList(
            ParseTypeHandle("Int32"),
            ParseTypeHandle("String")
        )
    )
); -- Tuple<Int32,String>

StructTypeComponents

Signature

StructTypeComponents(StructTypeHandle)->List<Struct<Name:String, Type:TypeHandle>>

Getting the item type handle list and their names from the structure type handle passed to the argument. The reverse function is StructTypeHandle.

Examples:

SELECT ListMap(
    StructTypeComponents(
        ParseTypeHandle("Struct<a:Int32, b:String>")
    ),
    ($x) -> {
        return AsTuple(
            FormatType($x.Type),
            $x.Name
        )
    }
); -- [("Int32","a"), ("String","b")]

StructTypeHandle

Signature

StructTypeHandle(List<Struct<Name:String, Type:TypeHandle>>)->structure type handle

Building a structure type handle from the item type handles and names passed to the argument as a list. The reverse function is StructTypeComponents.

Examples:

SELECT FormatType(
    StructTypeHandle(
        AsList(
            AsStruct(ParseTypeHandle("Int32") as Type,"a" as Name),
            AsStruct(ParseTypeHandle("String") as Type, "b" as Name)
        )
    )
); -- Struct<'a':Int32,'b':String>

DictTypeComponents

Signature

DictTypeComponents(DictTypeHandle)->Struct<Key:TypeHandle, Payload:TypeHandle>

Getting the type-key handle and the type-value handle from the dict type handle passed to the argument. The reverse function is DictTypeHandle.

Examples:

$d = DictTypeComponents(ParseTypeHandle("Dict<Int32,String>"));

SELECT
    FormatType($d.Key),     -- Int32
    FormatType($d.Payload); -- String

DictTypeHandle

Signature

DictTypeHandle(TypeHandle, TypeHandle)->dict type handle

Building a dict type handle from the type-key and type-value handle passed to the arguments. The reverse function is DictTypeComponents.

Examples:

SELECT FormatType(
    DictTypeHandle(
        ParseTypeHandle("Int32"),
        ParseTypeHandle("String")
    )
); -- Dict<Int32, String>

ResourceTypeTag

Signature

ResourceTypeTag(ResourceTypeHandle)->String

Getting the tag from the resource type handle passed to the argument. The reverse function is ResourceTypeHandle.

Examples:

SELECT ResourceTypeTag(ParseTypeHandle("Resource<foo>")); -- foo

ResourceTypeHandle

Signature

ResourceTypeHandle(String)->resource type handle

Building a resource type handle by the value of the tag passed to the argument. The reverse function is ResourceTypeTag.

Examples:

SELECT FormatType(ResourceTypeHandle("foo")); -- Resource<'foo'>

TaggedTypeComponents

Signature

TaggedTypeComponents(TaggedTypeHandle)->Struct<Base:TypeHandle, Tag:String>

Getting the tag and base type from the tagged type handle passed to the argument. The reverse function is TaggedTypeHandle.

Examples:

$t = TaggedTypeComponents(ParseTypeHandle("Tagged<Int32,foo>"));

SELECT FormatType($t.Base), $t.Tag; -- Int32, foo

TaggedTypeHandle

Signature

TaggedTypeHandle(TypeHandle, String)->tagged type handle

Building a tagged type handle by the base type handle and the tag name passed in the arguments. The reverse function is TaggedTypeComponents.

Examples:

SELECT FormatType(TaggedTypeHandle(
    ParseTypeHandle("Int32"), "foo"
)); -- Tagged<Int32, 'foo'>

VariantTypeHandle

Signature

VariantTypeHandle(StructTypeHandle)->variant type handle on top of structure
VariantTypeHandle(TupleTypeHandle)->variant type handle on top of tuple

Building a variant type handle by the underlying type handle passed to the argument. The reverse function is VariantUnderlyingType.

Examples:

SELECT FormatType(VariantTypeHandle(
    ParseTypeHandle("Tuple<Int32, String>")
)); -- Variant<Int32, String>

VoidTypeHandle and NullTypeHandle

Signature

VoidTypeHandle()->Void type handle
NullTypeHandle()->Null type handle

Building a Void and Null type handle, respectively.

Examples:

SELECT FormatType(VoidTypeHandle()); -- Void
SELECT FormatType(NullTypeHandle()); -- Null

CallableTypeComponents

Signature

CallableTypeComponents(CallableTypeHandle)->
Struct<
    Arguments:List<Struct<
        Flags:List<String>,
        Name:String,
        Type:TypeHandle>>,
    OptionalArgumentsCount:Uint32,
    Payload:String,
    Result:TypeHandle
>

Getting a description of the callable value type handle passed to the argument. The reverse function is CallableTypeHandle.

Examples:

$formatArgument = ($x) -> {
    return AsStruct(
        FormatType($x.Type) as Type,
        $x.Name as Name,
        $x.Flags as Flags
    )
};

$formatCallable = ($x) -> {
    return AsStruct(
        $x.OptionalArgumentsCount as OptionalArgumentsCount,
        $x.Payload as Payload,
        FormatType($x.Result) as Result,
        ListMap($x.Arguments, $formatArgument) as Arguments
    )
};

SELECT $formatCallable(
    CallableTypeComponents(
        ParseTypeHandle("(Int32,[bar:Double?{Flags:AutoMap}])->String")
    )
);  -- (OptionalArgumentsCount: 1, Payload: "", Result: "String", Arguments: [
    --   (Type: "Int32", Name: "", Flags: []),
    --   (Type: "Double?", Name: "bar", Flags: ["AutoMap"]),
    -- ])

CallableArgument

Signature

CallableArgument(TypeHandle, [String, [List<String>]])->Struct<Flags:List<String>,Name:String,Type:TypeHandle>

Packing the callable value argument description into the structure to pass to the CallableTypeHandle function based on the following arguments:

  1. Argument type handle.
  2. Optional argument name. The default value is an empty string.
  3. Optional argument flags as a list of strings. The default value is an empty list. Supported flags: "AutoMap".

CallableTypeHandle

Signature

CallableTypeHandle(TypeHandle, List<Struct<Flags:List<String>,Name:String,Type:TypeHandle>>, [Uint32, [String]])->callable value type handle

Building a callable value type handle based on the following arguments:

  1. Returned value type handle.
  2. A list of argument descriptions obtained via the CallableArgument function.
  3. Optional number of optional arguments in the callable value. The default value is 0.
  4. Optional tag for the callable value type. The default value is an empty string.

The reverse function is CallableTypeComponents.

Examples:

SELECT FormatType(
    CallableTypeHandle(
        ParseTypeHandle("String"),
        AsList(
            CallableArgument(ParseTypeHandle("Int32")),
            CallableArgument(ParseTypeHandle("Double?"), "bar", AsList("AutoMap"))
        ),
        1
    )
);  -- Callable<(Int32,['bar':Double?{Flags:AutoMap}])->String>

LambdaArgumentsCount

Signature

LambdaArgumentsCount(LambdaFunction)->Uint32

Getting the number of arguments in a lambda function.

Examples:

SELECT LambdaArgumentsCount(($x, $y)->($x+$y))
; -- 2

LambdaOptionalArgumentsCount

Signature

LambdaOptionalArgumentsCount(LambdaFunction)->Uint32

Getting the number of optional arguments in a lambda function.

Examples:

SELECT LambdaOptionalArgumentsCount(($x, $y, $z?)->(if($x,$y,$z)))
; -- 1
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