On 04/08/2019 05:59 AM, Ron Tarrant wrote:
On Monday, 8 April 2019 at 12:40:10 UTC, Adam D. Ruppe wrote:
You don't need template keyword for the majority of cases because the
compiler lets you do shortcuts.
Thanks, Adam. Good to know.
(maybe I am looking at the wrong part of the book, it is hard to find
the right section/page number online).
My bad. The edition I'm working from was released 2018-10-17 and can be
found here:
http://ddili.org/ders/d.en/Programming_in_D.pdf
The page number in online PDF viewer is 421 and the example is about 1/3
of the way down the page.
That template specialization works along with the general definition of
the same template. So, you must have the following function template as
well:
T getResponse(T)(string question) {
writef("%s (%s): ", question, T.stringof);
T response;
readf(" %s", &response);
return response;
}
As Steve said, when you replace all Ts in there e.g. with int, you get
what the compiler would generate for T being int. However, the readf
above cannot work with e.g. Point!double because readf does not know
what Point!double is. For that reason, we may use a specialization for
Point!T:
Point!T getResponse(T : Point!T)(string question)
{
writefln("%s (Point!%s)", question, T.stringof);
auto x = getResponse!T(" x");
auto y = getResponse!T(" y");
return(Point!T(x, y));
} // getResponse() Point!T
(It may be made to work with Adam's (T : Point!R, R) syntax but I failed
just now.)
Now you have a specialization that works with any Point!T. T can be
double, int, etc. However, you must call getResponse with that special
Point. I'm using an alias for code reduction:
alias MapLocation = Point!double;
auto wayPoint1 = getResponse!MapLocation("Where is the first map
location?");
auto wayPoint2 = getResponse!MapLocation("Where is the second map
location?");
Your code did not work because Point is not a type but a type template.
(On the other hand, Point!double is a type). The whole program:
import std.stdio;
import std.math;
import std.string;
struct Point(T)
{
T x;
T y;
T distanceTo(Point that) const
{
immutable real xDistance = x - that.x;
immutable real yDistance = y - that.y;
immutable distance = sqrt((xDistance * xDistance) + (yDistance
* yDistance));
return(cast(T)distance);
} // distanceTo()
} // struct Point
T getResponse(T)(string question) {
writef("%s (%s): ", question, T.stringof);
T response;
readf(" %s", &response);
return response;
}
Point!T getResponse(T : Point!T)(string question)
{
writefln("%s (Point!%s)", question, T.stringof);
auto x = getResponse!T(" x");
auto y = getResponse!T(" y");
return(Point!T(x, y));
} // getResponse() Point!T
void main()
{
alias MapLocation = Point!double;
auto wayPoint1 = getResponse!MapLocation("Where is the first map
location?");
auto wayPoint2 = getResponse!MapLocation("Where is the second map
location?");
writeln("Distance: ", wayPoint1.distanceTo(wayPoint2));
} // main()
Ali
