On Saturday, 7 July 2018 at 15:25:51 UTC, vino.B wrote:
Hi All,
If we replace the statement as args[$ -1] the program works
are expected, if we apply the same logic in different approach
it does not work, in the below code if we command the first
block "if (fnID == "ListFilesNames") {} " then the second "if
(fnID == "ListFilesSize") {}" works fine, and vice versa but if
both the "if" block is un-commented it does not work , rather
it passes wrong parameter to the function. Tried change the
args as args[$] , args[1], args[2],
Error:
Test.d(31): Error: function Test.ListFilesSize(string FFs, int
Size) is not callable using argument types (string,
Array!string)
VarTest.d(31): cannot pass argument _param_1 of type
Array!string to parameter int Size
Test.d(42): Error: template instance
`Test.process!(Array!string)` error instantiating
Code:
[...]
void process(T ...)(string fnID, T args) {
Throw in a pragma here:
void process(T ...)(string fnID, T args) {
pragma(msg, T);
...
}
[...]
void main() {
Array!string NameDir, SizeDir;
NameDir.insert("C:\\Temp\\BACKUP1");
SizeDir.insert("C:\\Temp\\TEAM1");
int Size = 1;
string fnID1 = "ListFilesNames", fnID2 = "ListFilesSize";
process(fnID1, NameDir); // 1
process(fnID2, SizeDir, Size); // 2
If you call '// 1' first, then the output would be
(Array!string)
... ERROR
and switch the order:
process(fnID2, SizeDir, Size); // 2
process(fnID1, NameDir); // 1
Now you'll see from the pragma output:
(Array!string, int)
(Array!string)
... ERROR
So the '// 2' call actually compiled fine.
The compiler complains because the function would try to call
ListFilesSize(int) with the parameter args[$-1], which in this
case would be the last element, so Array!string.
`args` is a compile time-construct. In effect you instantiate two
templates with the following calls:
process(fnID1, NameDir); // same as
process!(Array!string)(fnID1, NameDir)
instantiates the function
void process(string fnID, (Array!string) args) {
...
// accessing args[$-1] equals accessing args[0] (only one
element)
ListFilesSize(FFs, args[$ - 1]);
// above function will call ListFilesSize(string,
Array!string).. which does not exist, hence the error
}
and
process(fnID2, SizeDir, Size); // same as
process!(Array!string, int)(fnID1, NameDir, Size)
instantiates the function
void process(string fnID, (Array!string, int) args) {
...
// this time args.length == 2
// hence the call to args[$-1] == args[1] == int
ListFilesSize(FFs, args[$-1]); // compiles!!! args[$-1]
fits ListFilesSize signature!
It helps me to think in two domains. There is the "static" CT
(compile-time) and the RT (run-time) domain. You can vary how CT
code is laid out with "static" statements (such as "static if" or
"static foreach", or use aliases. Beware that "static this()" or
static functions are something different once again).
So you would have to determine _at compile time_ how the
'process' function should look given it's arguments:
void process(T ...)(T args)
{
static if (T.length == 1 && is(T[0] == Array!string))
{
// 1
}
else static if (T.length == 2 && is(T[0] == Array!string) &&
is(T[1] == int))
{
// 2
}
}
So in case above function get's called with only one argument
which is an Array!string, only the '// 1' part is left for the
run-time to be executed.
OR you could test if the function compiles
void process(T ...)(T args)
{
static if (is(typeof(ListFilesSize(args[$-1]))))
ListFilesSize(args[$-1]);
else
static assert(false);
}
Another option would be to use template constraints
void process(T ...)(T args)
if (is(typeof(ListFilesSize(args[$-1]))))
{
ListFilesSize(args[$-1]);
}
This is a nice chapter to read (in fact the whole book is a great
read):
http://ddili.org/ders/d.en/cond_comp.html
