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4.26.6 reference and shared related functions
def
- explicitly type casts to
reference or shared, respectively.
(Note: For the def declaration, see def.)
Example:
| | system("reference"); system("shared");
int i =1;
reference ref = i;
shared sh = 17;
list ll = list(ref, ref, ref, sh, sh);
ll[1] = 2; // replace only one entry
ll;
==> [1]:
==> 2
==> [2]:
==> 1
==>
==> [3]:
==> 1
==>
==> [4]:
==> 17
==>
==> [5]:
==> 17
==>
def(ll[2]) = 3; // change the others
ll;
==> [1]:
==> 2
==> [2]:
==> 3
==>
==> [3]:
==> 3
==>
==> [4]:
==> 17
==>
==> [5]:
==> 17
==>
def(ll[4]) = 19; // same here
ll;
==> [1]:
==> 2
==> [2]:
==> 3
==>
==> [3]:
==> 3
==>
==> [4]:
==> 19
==>
==> [5]:
==> 19
==>
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link
- explicitly dereference a
reference or shared object.
(Note: For the link declaration, see link.)
Example:
| | system("reference"); system("shared");
ring r = 0, (x,y,z), dp;
poly p = x + y + z;
def x_=x;
reference xref=x_;
xref;
==> x
==>
subst(p, xref,1, y,2, z,3); // fails
==> ? subst(`poly`,`reference`,`int`) failed
==> ? expected subst(`poly`,`poly`,`poly`)
==> ? expected subst(`poly`,`poly`,`poly`)
==> ? expected subst(`matrix`,`poly`,`int`)
==> ? error occurred in or before ./examples/reference_and_shared_related_\
functions_1.sing line 7: `subst(p, xref,1, y,2, z,3); // fails`
subst(p, link(xref),1, y,2, z,3); // fine
==> 6
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system
- The
reference and shared objects overload the
system command to gain extended features, see system(ref, "help")
for more details.
(Note: For the general system command, see system.)
Example:
| | system("reference"); system("shared");
shared sh;
system(sh, "help");
==> system(<ref>, ...): extended functionality for reference/shared data <ref\
>
==> system(<ref>, count) - number of references pointing to <ref>
==> system(<ref>, enumerate) - unique number for identifying <ref>
==> system(<ref>, undefined) - checks whether <ref> had been assigned
==> system(<ref>, "help") - prints this information message
==> system(<ref>, "typeof") - actual type referenced by <ref>
==> system(<ref1>, same, <ref2>) - tests for identic reference objects
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