Difference between revisions of "pas2js Generics"

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*** FPC/pas2js: allowed for valid combinations -> operators are checked on specialization, Note: because of implementation cross uses, check is delayed until used unit implementation is complete
 
*** FPC/pas2js: allowed for valid combinations -> operators are checked on specialization, Note: because of implementation cross uses, check is delayed until used unit implementation is complete
 
** for-in TWithConstraint
 
** for-in TWithConstraint
 +
** typeinfo(T)
  
 
==ToDos==
 
==ToDos==
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** T as TFoo<Integer>
 
** T as TFoo<Integer>
 
** TFoo<Integer>(expr)
 
** TFoo<Integer>(expr)
** typeinfo(T)
 
 
** call
 
** call
 
*** Delphi: must fit the constraint. For example without constraint it only fits untyped args.
 
*** Delphi: must fit the constraint. For example without constraint it only fits untyped args.

Revision as of 16:34, 8 September 2019

Overview

Pas2js will support FPC and Delphi like generics.

The next goal is to support more statements, see below

Working

  • generic record
  • specialize:
    • ObjFPC: type TFoo = specialize TGen<word>;
    • Delphi: type TFoo = TGen<word>;
    • ObjFPC anonymous: var r: specialize TBird<word>;
    • Delphi: anonymous var r: TBird<word>;
  • generic class
    • specialize in ancestor type
    • forward generic class (FPC 3.3.1 does not support it yet)
    • enumtype inside generic is not propagated
  • generic external class
  • 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 interface
  • generic procedural type
    • specialized proc types can assign normal proc
  • Delphi type overload, e.g. type TArr = array of word; TArr<T> = array of T; TArr<T,S> = record i:T; j:S end;
  • anonymous type in specialize: TBird<array of word>
  • nested specialize: TBird<TWing<byte>>
  • record/class field
  • property
  • method (not confused with generic method)
    • Delphi: implementation must repeat type params, must omit constraints
    • FPC: implementation must not repeat type params
  • for-loop, if-then-else, repeat-until, while-do, try-finally, try-except, case-of
  • some assignments
  • primitive expression like identifiers and constants
  • operators: +, -
  • constraints:
    • keyword record, class, constructor checked at specialization
    • class type checked at specialization
  • constraints:
    • "class":
      • Delphi/FPC: T is TObject
      • pas2js: test if T is a class, either TObject or an external class
    • "constructor": test if T is TObject and Create resolves to TObject.create
    • "record": test if T is a record type
    • class type: test if param fits
    • list of interface types: test if param fits
    • forward class must repeat constraints
    • Delphi does not allow TObject as constraint. pas2js allows it, because it has other root classes.
    • constraint refers to prior template name: type TBird<X, Y: TAnt<X>> = record a: X; b: Y; end;
  • statements:
    • specialize (cloning) all kinds of statements and expressions
    • inline specialize expression, e.g. TList<word>.Create
      • Delphi: TFoo<Integer>.Create
      • FPC: specialize TFoo<Integer>.Create
    • "obj is T": allowed with constraint "class" or class type
    • typecast T(): allowed with constraint "class" or class type
    • 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
      • Pas2js: allowed
    • anInt:=GenericVar
      • Delphi: always Error: Incompatible types: 'Integer' and 'T'
      • FPC/pas2js: allowed for valid combinations -> operators are checked on specialization, Note: because of implementation cross uses, check is delayed until used unit implementation is complete
    • for-in TWithConstraint
    • typeinfo(T)

ToDos

  • nested generic type: allowed by Delphi, not allowed by FPC
  • cascaded specialize: TBird<word>.TWing<byte>
  • generic class:
    • default classname "TTest<System.Longint>"
    • pas2js classname "TTest$G1" and overloads
    • Delphi: descendants cannot refer to type parameters of ancestors
    • members can refer to itself without parameters
  • 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
  • specialize method:
    • explicitly specifying Fly<word>(aWord)
    • automatic inferring types Fly(aWord), $modeswitch implicitfunctionspecialization MyProc(1) calls MyProc<T>(a: T)
  • Statements:
    • T is TFoo<Integer>
    • T as TFoo<Integer>
    • TFoo<Integer>(expr)
    • call
      • Delphi: must fit the constraint. For example without constraint it only fits untyped args.
      • FPC: if only one function in scope preselect it, overloads are selected by constraints alone. Later checked by specialization.
  • nicer error messages
    • instead of TList$G1 write TList<word>
    • write a hint where it was specialized
  • filer
  • optimization: reuse specialized functions
  • constants as templates: Not planned