pas2js Generics

Overview

Working

• Simple generic record with simple members name:T

ToDos

• Delphi type overload, e.g. type TArr = array of word; TArr<T> = array of T; TArr<T,S> = record i:T; j:S end;
• cascaded specialize: TBird<word>.TWing<byte>
• nested specialize: TBird<TWing<byte>>
• anonymous type in specialize: TBird<array of word>
• generic class:
  • default classname "TTest<System.Longint>"
  • pas2js classname "TTest$G1" and overloads
  • descendants cannot refer to type parameters of ancestors
  • members can refer to itself without parameters:
  • enumtype inside generic is not propagated
  • nested generic: allowed by Delphi, not allowed by FPC
  • method implementation
    • Delphi: must repeat type params, can omit constraints
    • FPC: must not repeat type params
  • forward class (FPC does support it yet)
• generic record:
• generic interface:
• generic array:
• generic static array: Note: delphi wiki says "no static arrays", but 10.3 compiles it, see http://docwiki.embarcadero.com/RADStudio/Rio/en/Declaring_Generics
• generic procedural type:
• generic function (aka parametrized method):
  • Delphi does not allow global generic functions, only generic methods
  • methods: virtual, message, constructor and destructors cannot have type parameters
• constraints:
  • "class", "record", "constructor" (class+default constructor, can be combined with class)
  • multiple interface types
  • one class type (Delphi: not TObject)
  • forward class must repeat constraints
• specialize method:
  • explicitly specifying Fly<word>(aWord)
  • automatic inferring types Fly(aWord), $modeswitch implicitfunctionspecialization MyProc(1) calls MyProc<T>(a: T)
• specialized proc types can assign normal proc
• Statements:
  • inline specialization
    • Delphi: TFoo<Integer>.Create
    • FPC: specialize TFoo<Integer>.Create
  • T is TFoo<Integer>
  • T as TFoo<Integer>
  • TFoo<Integer>(expr)
  • "obj is T": allowed with constraint "class" or class type
  • typecast T(): allowed with constraint "class" or class type
  • typeinfo(T)
  • using implementation function in generic function:
    • Delphi: Error: Method of parameterized type declared in interface section must not use local symbol '%s'
    • FPC: Error: Global Generic template references static symtable
  • anInt:=GenericVar
    • Delphi: always Error: Incompatible types: 'Integer' and 'T'
    • FPC: allowed for valid combinations -> operators are checked on specialization, Note: because of implementation cross uses, check must be delayed until used unit implementation is complete
  • call
    • Delphi: must fit the constraint. For example without constraint it only fits untyped args.
    • FPC: if only one function in scope preselect it, overloads are selected by constraints alone. Later checked by specialization.