Asymptote
implicitly casts int
to real
, int
to
pair
, real
to pair
, pair
to path
,
pair
to guide
, path
to guide
, guide
to path
, and real
to pen
. Implicit casts are
also automatically attempted when trying to match function calls with
possible function signatures. Implicit casting can be inhibited
by declaring individual arguments explicit
in the function
signature, say to avoid an ambiguous function call in the following
example, which outputs 0:
int f(pair a) {return 0;} int f(explicit real x) {return 1;} write(f(0));
Other conversions, say real
to int
or
real
to string
, require an explicit cast:
int i=(int) 2.5; string s=(string) 2.5; real[] a={2.5,-3.5}; int[] b=(int []) a; write(stdout,b); // Outputs 2,-3
Casting to user-defined types is also possible using operator cast
:
struct rpair { public real radius; public real angle; } rpair operator init() {return new rpair;} pair operator cast(rpair x) { return (x.radius*cos(x.angle),x.radius*sin(x.angle)); } rpair x; x.radius=1; x.angle=pi/6; write(x); // Outputs (0.866025403784439,0.5)
One must use care when defining new cast operators. Suppose that in some code one wants all integers to represent multiples of 100. To convert them to reals, one would first want to multiply them by 100. However, the straightforward implementation
real operator cast(int x) {return x*100;}is equivalent to an infinite recursion, since the result
x*100
needs itself to be cast from an integer to a real. Instead, we want to
use the standard conversion of int to real:
real convert(int x) {return x*100;} real operator cast(int x)=convert;
Explicit casts are implemented similarly, with operator ecast
.