src/kernel/class.jam

# Copyright 2001, 2002, 2003 Dave Abrahams
# Copyright 2002, 2005 Rene Rivera
# Copyright 2002, 2003 Vladimir Prus
# Distributed under the Boost Software License, Version 1.0.
# (See accompanying file LICENSE_1_0.txt or copy at
# http://www.boost.org/LICENSE_1_0.txt)

# Polymorphic class system built on top of core Jam facilities.
#
# Classes are defined by 'class' keywords:
#
#     class myclass
#     {
#         rule __init__ ( arg1 )     # constructor
#         {
#             self.attribute = $(arg1) ;
#         }
#
#         rule method1 ( )           # method
#         {
#             return [ method2 ] ;
#         }
#
#         rule method2 ( )           # method
#         {
#             return $(self.attribute) ;
#         }
#     }
#
# The __init__ rule is the constructor, and sets member variables.
#
# New instances are created by invoking [ new <class> <args...> ]:
#
#     local x = [ new myclass foo ] ;        # x is a new myclass object
#     assert.result foo : [ $(x).method1 ] ; # $(x).method1 returns "foo"
#
# Derived class are created by mentioning base classes in the declaration::
#
#     class derived : myclass
#     {
#          rule __init__ ( arg )
#          {
#              myclass.__init__ $(arg) ;  # call base __init__
#
#          }
#
#          rule method2 ( )           # method override
#          {
#              return $(self.attribute)XXX ;
#          }
#     }
#
# All methods operate virtually, replacing behavior in the base classes. For
# example::
#
#     local y = [ new derived foo ] ;            # y is a new derived object
#     assert.result fooXXX : [ $(y).method1 ] ;  # $(y).method1 returns "foo"
#
# Each class instance is its own core Jam module. All instance attributes and
# methods are accessible without additional qualification from within the class
# instance. All rules imported in class declaration, or visible in base classes
# are also visible. Base methods are available in qualified form:
# base-name.method-name. By convention, attribute names are prefixed with
# "self.".

import modules ;
import numbers ;


rule xinit ( instance : class )
{
    module $(instance)
    {
        __class__ = $(2) ;
        __name__ = $(1) ;
    }
}


rule new ( class args * : * )
{
    .next-instance ?= 1 ;
    local id = object($(class))@$(.next-instance) ;

    INSTANCE $(id) : class@$(class) ;
    xinit $(id) : $(class) ;
    IMPORT_MODULE $(id) ;
    $(id).__init__ $(args) : $(2) : $(3) : $(4) : $(5) : $(6) : $(7) : $(8) :
        $(9) : $(10) : $(11) : $(12) : $(13) : $(14) : $(15) : $(16) : $(17) :
        $(18) : $(19) ;

    # Bump the next unique object name.
    .next-instance = [ numbers.increment $(.next-instance) ] ;

    # Return the name of the new instance.
    return $(id) ;
}


rule bases ( class )
{
    module class@$(class)
    {
        return $(__bases__) ;
    }
}


rule is-derived ( class : bases + )
{
    local stack = $(class) ;
    local visited found ;
    while ! $(found) && $(stack)
    {
        local top = $(stack[1]) ;
        stack = $(stack[2-]) ;
        if ! ( $(top) in $(visited) )
        {
            visited += $(top) ;
            stack += [ bases $(top) ] ;

            if $(bases) in $(visited)
            {
                found = true ;
            }
        }
    }
    return $(found) ;
}


# Returns true if the 'value' is a class instance.
#
rule is-instance ( value )
{
    return [ MATCH "^(object\\()[^@]+\\)@.*" : $(value) ] ;
}


# Check if the given value is of the given type.
#
rule is-a (
    instance  # The value to check.
    : type  # The type to test for.
)
{
    if [ is-instance $(instance) ]
    {
        return [ class.is-derived [ modules.peek $(instance) : __class__ ] : $(type) ] ;
    }
}


local rule typecheck ( x )
{
    local class-name = [ MATCH "^\\[(.*)\\]$" : [ BACKTRACE 1 ] ] ;
    if ! [ is-a $(x) : $(class-name) ]
    {
        return "Expected an instance of "$(class-name)" but got \""$(x)"\" for argument" ;
    }
}


rule __test__ ( )
{
    import assert ;
    import "class" : new ;
    import errors : try catch ;

    # This will be the construction function for a class called 'myclass'.
    #
    class myclass
    {
        import assert ;

        rule __init__ ( x_ * : y_ * )
        {
            # Set some instance variables.
            x = $(x_) ;
            y = $(y_) ;
            foo += 10 ;
        }

        rule set-x ( newx * )
        {
            x = $(newx) ;
        }

        rule get-x ( )
        {
            return $(x) ;
        }

        rule set-y ( newy * )
        {
            y = $(newy) ;
        }

        rule get-y ( )
        {
            return $(y) ;
        }

        rule f ( )
        {
            return [ g $(x) ] ;
        }

        rule g ( args * )
        {
            if $(x) in $(y)
            {
                return $(x) ;
            }
            else if $(y) in $(x)
            {
                return $(y) ;
            }
            else
            {
                return ;
            }
        }

        rule get-class ( )
        {
            return $(__class__) ;
        }

        rule get-instance ( )
        {
            return $(__name__) ;
        }

        rule invariant ( )
        {
            assert.equal 1 : 1 ;
        }

        rule get-foo ( )
        {
            return $(foo) ;
        }
    }  # class myclass ;

    class derived1 : myclass
    {
        rule __init__ ( z_ )
        {
            myclass.__init__ $(z_) : X ;
            z = $(z_) ;
        }

        # Override g.
        #
        rule g ( args * )
        {
            return derived1.g ;
        }

        rule h ( )
        {
            return derived1.h ;
        }

        rule get-z ( )
        {
            return $(z) ;
        }

        # Check that 'assert.equal' visible in base class is visible here.
        #
        rule invariant2 ( )
        {
            assert.equal 2 : 2 ;
        }

        # Check that 'assert.variable-not-empty' visible in base class is
        # visible here.
        #
        rule invariant3 ( )
        {
            local v = 10 ;
            assert.variable-not-empty v ;
        }
    }  # class derived1 : myclass ;

    class derived2 : myclass
    {
        rule __init__ ( )
        {
            myclass.__init__ 1 : 2 ;
        }

        # Override g.
        #
        rule g ( args * )
        {
            return derived2.g ;
        }

        # Test the ability to call base class functions with qualification.
        #
        rule get-x ( )
        {
            return [ myclass.get-x ] ;
        }
    }  # class derived2 : myclass ;

    class derived2a : derived2
    {
        rule __init__
        {
            derived2.__init__ ;
        }
    }  # class derived2a : derived2 ;

    local rule expect_derived2 ( [derived2] x ) { }

    local a = [ new myclass 3 4 5 : 4 5 ] ;
    local b = [ new derived1 4 ] ;
    local b2 = [ new derived1 4 ] ;
    local c = [ new derived2 ] ;
    local d = [ new derived2 ] ;
    local e = [ new derived2a ] ;

    expect_derived2 $(d) ;
    expect_derived2 $(e) ;

    # Argument checking is set up to call exit(1) directly on failure, and we
    # can not hijack that with try, so we should better not do this test by
    # default. We could fix this by having errors look up and invoke the EXIT
    # rule instead; EXIT can be hijacked (;-)
    if --fail-typecheck in [ modules.peek : ARGV ]
    {
        try ;
        {
            expect_derived2 $(a) ;
        }
        catch
            "Expected an instance of derived2 but got" instead
            ;
    }

    #try ;
    #{
    #    new bad_subclass ;
    #}
    #catch
    #    bad_subclass.bad_subclass failed to call base class constructor
    #        myclass.__init__
    #  ;

    #try ;
    #{
    #    class bad_subclass ;
    #}
    #catch bad_subclass has already been declared ;

    assert.result 3 4 5 : $(a).get-x ;
    assert.result 4 5 : $(a).get-y ;
    assert.result 4 : $(b).get-x ;
    assert.result X : $(b).get-y ;
    assert.result 4 : $(b).get-z ;
    assert.result 1 : $(c).get-x ;
    assert.result 2 : $(c).get-y ;
    assert.result 4 5 : $(a).f ;
    assert.result derived1.g : $(b).f ;
    assert.result derived2.g : $(c).f ;
    assert.result derived2.g : $(d).f ;

    assert.result 10 : $(b).get-foo ;

    $(a).invariant ;
    $(b).invariant2 ;
    $(b).invariant3 ;

    # Check that the __class__ attribute is getting properly set.
    assert.result myclass : $(a).get-class ;
    assert.result derived1 : $(b).get-class ;
    assert.result $(a) : $(a).get-instance ;

    $(a).set-x a.x ;
    $(b).set-x b.x ;
    $(c).set-x c.x ;
    $(d).set-x d.x ;
    assert.result a.x : $(a).get-x ;
    assert.result b.x : $(b).get-x ;
    assert.result c.x : $(c).get-x ;
    assert.result d.x : $(d).get-x ;

    class derived3 : derived1 derived2
    {
        rule __init__ ( )
        {
        }
    }

    assert.result : bases myclass ;
    assert.result myclass : bases derived1 ;
    assert.result myclass : bases derived2 ;
    assert.result derived1 derived2 : bases derived3 ;

    assert.true is-derived derived1 : myclass ;
    assert.true is-derived derived2 : myclass ;
    assert.true is-derived derived3 : derived1 ;
    assert.true is-derived derived3 : derived2 ;
    assert.true is-derived derived3 : derived1 derived2 myclass ;
    assert.true is-derived derived3 : myclass ;

    assert.false is-derived myclass : derived1 ;

    assert.true is-instance $(a) ;
    assert.false is-instance bar ;

    assert.true is-a $(a) : myclass ;
    assert.true is-a $(c) : derived2 ;
    assert.true is-a $(d) : myclass ;
    assert.false is-a literal : myclass ;
}