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4.23.1 Definition of a user defined type
- Syntax:
newstruct( name , string_expression );
newstruct( name , name , string_expression );
- Purpose:
- defines a new type with elements given by the last argument (string_expression).
The name of the new type is the first argument (of type string) and must
be longer than one character.
The second name (of type string) is an already defined type
which should be extended by the new type.
The last argument (of type string) must be an comma separated list of
a type followed by a name.
If there are duplicate member names, the last one wins.
(User defined) member names are restricted to alphanumeric charecters and must start with a letter.
- Operations:
- the only operations of user defined types are:
- assignment (between objects of the same or extended type)
typeof
string and printing
- operator
. to access the elements
- Example:
| | newstruct("nt","int a,poly b,string c");
nt A;
nt B;
A.a=3;
A.c=string(A.a);
B=A;
newstruct("t2","nt","string c");
t2 C; C.c="t2-c";
A=C;
typeof(A);
==> t2
A;
==> c=t2-c
==> c=
==> b=??
==> a=0
// a motivating example ------------------------------------------
newstruct("IDEAL","ideal I,proc prettyprint");
newstruct("HOMOGENEOUS_IDEAL","IDEAL","intvec weights,proc prettyprint");
proc IDEAL_pretty_print(IDEAL I)
{
"ideal generated by";
I.I;
}
proc H_IDEAL_pretty_print(HOMOGENEOUS_IDEAL I)
{
"homogeneous ideal generated by";
I.I;
"with weights";
I.weights;
}
proc p_print(IDEAL I) { I.prettyprint(I); }
ring r;
IDEAL I;
I.I=ideal(x+y2,z);
I.prettyprint=IDEAL_pretty_print;
HOMOGENEOUS_IDEAL H;
H.I=ideal(x,y,z);
H.prettyprint=H_IDEAL_pretty_print;
H.weights=intvec(1,1,1);
p_print(I);
==> ideal generated by
==> _[1]=y2+x
==> _[2]=z
p_print(H);
==> homogeneous ideal generated by
==> _[1]=x
==> _[2]=y
==> _[3]=z
==> with weights
==> 1,1,1
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