Add a variable to a class instance at runtime: Difference between revisions

=={{header|Icon}} and {{header|Unicon}}==

{{omit from|Icon}}

Unicon implements object environments with records and supporting procedures for creation, initialization, and methods. To modify an instance you must create a new record then copy and amend it. The procedures ''constructor'' and ''fieldnames'' are needed. This example doesn't do error checking. Here ''extend'' takes three arguments, the class instance, a list of new variable names as strings, and an optional list of new values to be assigned.

''Note:'' Unicon can be translated via a command line switch into icon which allows for classes to be shared with Icon code (assuming no other incompatibilities exist).

<lang unicon>

link ximage

procedure main()

c1 := foo(1,2) # instance of foo

write("c1:\n",ximage(c1))

c1 := extend(c1,["c","d"],[8,9]) # 2 new fields

write("new c1:\n",ximage(c1))

c1 := extend(c1,["e"],[7]) # 1 more

write("newest c1:\n",ximage(c1))

end

class foo(a,b) # dummy class

end

procedure extend(instance,newvars,newvals) #: extend a class instance

every put(f := [],fieldnames(instance)) # copy existing fieldnames

c := ["tempconstructor"] ||| f # new constructor

every put(c,!newvars) # append new vars

t := constructor!c # new constructor

x := t() # new instance

every x[v := !f] := instance[v] # same as old instance

x.__s := x # new self

if \newvals then

every i := 1 to min(*newvars,*newvals) do

x[newvars[i]] := newvals[i] # add new vars = values

return x

end</lang>

{{libheader|Icon Programming Library}}

[http://www.cs.arizona.edu/icon/library/src/procs/ximage.icn ximage.icn provides ximage to dump variable contents]

Output:<pre>c1:

R_foo__state_1 := foo__state()

R_foo__state_1.a := 1

R_foo__state_1.b := 2

new c1:

R_tempconstructor_1 := tempconstructor()

R_tempconstructor_1.__s := R_tempconstructor_1

R_tempconstructor_1.__m := R_foo__methods_1 := foo__methods()

R_tempconstructor_1.a := 1

R_tempconstructor_1.b := 2

R_tempconstructor_1.c := 8

R_tempconstructor_1.d := 9

newest c1:

R_tempconstructor_1 := tempconstructor()

R_tempconstructor_1.__s := R_tempconstructor_1

R_tempconstructor_1.__m := R_foo__methods_1 := foo__methods()

R_tempconstructor_1.a := 1

R_tempconstructor_1.b := 2

R_tempconstructor_1.c := 8

R_tempconstructor_1.d := 9

R_tempconstructor_1.e := 7</pre>