SelectType¶
A select type construct: dispatch on the dynamic type of a polymorphic object.
Declaration¶
Syntax¶
SelectType(expr selector, identifier? assoc_name, type_stmt* body,
stmt* default)
Arguments¶
Argument |
Description |
|---|---|
|
the polymorphic object being examined. |
|
the name the selector is known by inside the branches, with the branch’s type; |
|
the branches, each a type_stmt. |
|
the statements of |
Return values¶
None.
Description¶
The branches are type is, which matches one dynamic type exactly, and
class is, which matches a type or anything extending it. They are
TypeStmtName and ClassStmt respectively, and
at most one runs.
Inside a branch the selector has the branch’s type rather than the declared polymorphic type, which is what makes the construct useful: a component of the extending type can be named there and nowhere else.
Examples¶
An ASR text document that uses it:
(TranslationUnit
:symtab (SymbolTable
:id 0
:symbols {
"m" (Module
:symtab (SymbolTable
:id 1
:symbols {
"circle" (Struct
:symtab (SymbolTable
:id 2
:symbols {
"r" (Variable
:parent_symtab 2
:name "r"
:dependencies []
:intent :Local
:symbolic_value nil
:value nil
:storage :Default
:type (Real
:kind 4
)
:type_declaration nil
:abi :Source
:access :Public
:presence :Required
:value_attr false
:target_attr false
:contiguous_attr false
:bindc_name nil
:is_volatile false
:is_protected false
:pass_attr :NotMethod
:self_argument nil
:codims []
)
}
)
:name "circle"
:struct_signature (StructType
:data_member_types [
(Real
:kind 4
)
]
:member_function_types []
:is_cstruct false
:is_unlimited_polymorphic false
)
:dependencies []
:members [
"r"
]
:member_functions []
:abi :Source
:access :Public
:is_packed false
:is_abstract false
:is_sequence false
:initializers []
:alignment nil
:parent (SymbolRef 1 "shape")
:kind_params []
)
"shape" (Struct
:symtab (SymbolTable
:id 3
:symbols {}
)
:name "shape"
:struct_signature (StructType
:data_member_types []
:member_function_types []
:is_cstruct false
:is_unlimited_polymorphic false
)
:dependencies []
:members []
:member_functions []
:abi :Source
:access :Public
:is_packed false
:is_abstract true
:is_sequence false
:initializers []
:alignment nil
:parent nil
:kind_params []
)
}
)
:name "m"
:parent_module nil
:dependencies []
:loaded_from_mod false
:intrinsic false
:has_submodules false
)
"main" (Program
:symtab (SymbolTable
:id 4
:symbols {
"c" (Variable
:parent_symtab 4
:name "c"
:dependencies []
:intent :Local
:symbolic_value nil
:value nil
:storage :Default
:type (StructType
:data_member_types [
(Real
:kind 4
)
]
:member_function_types []
:is_cstruct false
:is_unlimited_polymorphic false
)
:type_declaration (SymbolRef 4 "circle")
:abi :Source
:access :Public
:presence :Required
:value_attr false
:target_attr false
:contiguous_attr false
:bindc_name nil
:is_volatile false
:is_protected false
:pass_attr :NotMethod
:self_argument nil
:codims []
)
"circle" (ExternalSymbol
:parent_symtab 4
:name "circle"
:external (SymbolRef 1 "circle")
:module_name "m"
:scope_names []
:original_name "circle"
:access :Public
)
"s" (Variable
:parent_symtab 4
:name "s"
:dependencies []
:intent :Local
:symbolic_value nil
:value nil
:storage :Default
:type (Pointer
:type (StructType
:data_member_types []
:member_function_types []
:is_cstruct false
:is_unlimited_polymorphic false
)
)
:type_declaration (SymbolRef 4 "shape")
:abi :Source
:access :Public
:presence :Required
:value_attr false
:target_attr false
:contiguous_attr false
:bindc_name nil
:is_volatile false
:is_protected false
:pass_attr :NotMethod
:self_argument nil
:codims []
)
"shape" (ExternalSymbol
:parent_symtab 4
:name "shape"
:external (SymbolRef 1 "shape")
:module_name "m"
:scope_names []
:original_name "shape"
:access :Public
)
"x" (Variable
:parent_symtab 4
:name "x"
:dependencies []
:intent :Local
:symbolic_value nil
:value nil
:storage :Default
:type (Real
:kind 4
)
:type_declaration nil
:abi :Source
:access :Public
:presence :Required
:value_attr false
:target_attr false
:contiguous_attr false
:bindc_name nil
:is_volatile false
:is_protected false
:pass_attr :NotMethod
:self_argument nil
:codims []
)
}
)
:name "main"
:dependencies [
"m"
]
:body [
(SelectType
:selector (Var
:v (SymbolRef 4 "s")
)
:assoc_name "c"
:body [
(TypeStmtName
:sym (SymbolRef 4 "circle")
:body [
(Assignment
:target (Var
:v (SymbolRef 4 "x")
)
:value (RealConstant
:r 1.0
:type (Real
:kind 4
)
)
:overloaded nil
:realloc_lhs false
:move_allocation false
)
]
)
(ClassStmt
:sym (SymbolRef 4 "shape")
:body [
(Assignment
:target (Var
:v (SymbolRef 4 "x")
)
:value (RealConstant
:r 2.0
:type (Real
:kind 4
)
)
:overloaded nil
:realloc_lhs false
:move_allocation false
)
]
)
(TypeStmtType
:type (Real
:kind 4
)
:body [
(Assignment
:target (Var
:v (SymbolRef 4 "x")
)
:value (RealConstant
:r 3.0
:type (Real
:kind 4
)
)
:overloaded nil
:realloc_lhs false
:move_allocation false
)
]
)
]
:default [
(Assignment
:target (Var
:v (SymbolRef 4 "x")
)
:value (RealConstant
:r 0.0
:type (Real
:kind 4
)
)
:overloaded nil
:realloc_lhs false
:move_allocation false
)
]
)
]
)
}
)
:items []
)