Re: CTFE template predicates
template startsNotWith(string s,char c){
enum startsNotWith = s.length == 0 || s[0] != c;
}
Better still:
enum startsNotWith(string s, char c) = { return s.length == 0 ||
s[0] != c; }
Re: CTFE template predicates
On 2015-05-04 03:52:21 +, Rikki Cattermole said: Have you looked at my book? https://leanpub.com/ctfe No, thanks for the hint. You will have one more reader ;-) -- Robert M. Münch http://www.saphirion.com smarter | better | faster
Re: CTFE template predicates
On 2015-05-03 23:28:00 +, anonymous said:
Here T would have to be a type. But you want to accept a string. So:
template startsNotWith(string s,char c){
enum startsNotWith = s.length == 0 || s[0] != c;
}
Hi, ok, just to better understand this (I have a C++ background (even
quite old)): When I want to use some functions I need to specify the
type? It's not possible to use T.length() which would compile if T is a
string? I thought that it's just generic and I can throw in T.
1. How do predicates get their argument(s)? I saw code where only the
predicate was mentioned but no arguments. So, I assume there is some
behind-the-curtain-magic going on. I read about things like a == b
where I can reference 'a and 'b in a string.
Predicates are called/instantiated by the thing to which you pass them.
StaticFilter instantiates pred for each element of the T tuple it's
given. If some documentation doesn't say how the predicate will be
called/instantiated, then it's probably assumed to be obvious.
Well, and often it's obvious that it's not obvious ;-)
String predicates are turned into functions behind the curtains. The
thing you instantiate with a == b turns it into `(a, b) {return a ==
b;}` and uses that. I think we don't do string predicates for templates
like StaticFilter, though.
Ok, that helps to better understand how this works.
Thanks for the feedback.
--
Robert M. Münch
http://www.saphirion.com
smarter | better | faster
Re: CTFE template predicates
On 2015-05-03 23:28:00 +, anonymous said:
You need to turn T into a parameter, so that StaticFilter can set it.
(And it's really a string again, so I'm renaming to s.)
template startsNotWithp(string s)
{
enum startsNotWithp = startsNotWith!(s, 'p');
}
/* Shorthand syntax: enum startsNotWithp(string s) = startsNotWith!(s, 'p'); */
alias rules = StaticFilter!(startsNotWithp, org_rules);
Hi, I have one more questions: Is it possible to write something like this?
alias rules = StaticFilter!(startsNotWith(?, 'p'), org_rules);
The ? should be used for every memember of org_rules.
--
Robert M. Münch
http://www.saphirion.com
smarter | better | faster
Re: CTFE template predicates
On Monday, 4 May 2015 at 11:22:16 UTC, Robert M. Münch wrote:
Hi, ok, just to better understand this (I have a C++ background
(even quite old)): When I want to use some functions I need to
specify the type? It's not possible to use T.length() which
would compile if T is a string? I thought that it's just
generic and I can throw in T.
In template parameter lists, a solitary identifier is a type
parameter. You can only pass types in those.
In function (pointer) declarations, a solitary identifier is the
type of the parameter.
In function/delegate literals, a solitary identifier is the name
of the parameter and the type is inferred. I guess this is what
you were thinking of.
void main()
{
template t(T) {} /* T is a template type parameter. */
alias i = t!int; /* It can be instantiated with the type int,
for example, */
static assert(!__traits(compiles, t!123)); /* but not with a
value. */
void function(int) fp; /* int is the type of the parameter. */
fp = (x) {}; /* x is the name of the parameter whose type is
inferred from above. */
}
Re: CTFE template predicates
On 4/05/2015 11:15 p.m., Robert M. Münch wrote: On 2015-05-04 03:52:21 +, Rikki Cattermole said: Have you looked at my book? https://leanpub.com/ctfe No, thanks for the hint. You will have one more reader ;-) I'm currently live streaming, feel free to jump on and ask any questions! https://www.livecoding.tv/alphaglosined/
Re: CTFE template predicates
On Monday, 4 May 2015 at 11:41:23 UTC, Robert M. Münch wrote: Hi, I have one more questions: Is it possible to write something like this? alias rules = StaticFilter!(startsNotWith(?, 'p'), org_rules); The ? should be used for every memember of org_rules. No, we don't have template literals.
Re: CTFE template predicates
On 2015-05-04 03:52:21 +, Rikki Cattermole said: Have you looked at my book? https://leanpub.com/ctfe I bought it. Will it be updated? It's very generic with respect the concept and I'm missing code examples for all the user-cases. Especially the generator part is IMO very interesting. -- Robert M. Münch http://www.saphirion.com smarter | better | faster
Re: CTFE template predicates
On 5/05/2015 6:24 a.m., Robert M. Münch wrote: On 2015-05-04 03:52:21 +, Rikki Cattermole said: Have you looked at my book? https://leanpub.com/ctfe I bought it. Will it be updated? It's very generic with respect the concept and I'm missing code examples for all the user-cases. Especially the generator part is IMO very interesting. It's due for an update. Basically I just need to be told what people want. Otherwise I'll be doing it blind!
CTFE template predicates
Hi, I have now played a around couple of hours (reading everything I
could find) to get something to work, but I think I'm missing some
basic concepts/understanding. Maybe someone can enlighten me how these
things work. I thought that some code from David Nadlinger is what I'm
searching for but don't know how to exactly make use of it.
Here is the code: I want to filter out some of the allMembers and use
them in my code for a switch/final to check that call cases that were
not filtered are covered. Trying to build the enum for the switch/final
statement.
auto org_rules = TypeTuple!(__traits(allMembers,BolSource));
static assert(!isTypeTuple!(org_rules));
template startsNotWith(T,char C){
static if (T[0] != C){
enum startsNotWith = true;
} else {
enum startsNotWith = false;
}
}
template StaticFilter(alias pred, T...) {
static if (T.length == 0) {
alias TypeTuple!() StaticFilter;
} else static if (pred!(T[0])) {
alias TypeTuple!(T[0], StaticFilter!(pred, T[1 .. $])) StaticFilter;
} else {
alias StaticFilter!(pred, T[1 .. $]) StaticFilter;
}
}
alias startsNotWithp = startsNotWith!(T,p); // doesn't compile:
Error: undefined identifier T
alias rules = StaticFilter!(startsNotWithp, org_rules);
While playing with this a couple of questions came up:
1. How do predicates get their argument(s)? I saw code where only the
predicate was mentioned but no arguments. So, I assume there is some
behind-the-curtain-magic going on. I read about things like a == b
where I can reference 'a and 'b in a string.
2. enum startsNotwith = false So this is the return syntax for a CTFE
for return(true) ?
3. TupleType is a very missleading name when you are learning these
things, because the tuple can hold values as well. Or is there a more
extensive explanation for the name I don't get?
4. Are there any tutorials about CTFE? This seems to be a very powerful
but not so easy to use feature of D, but documentation is quite limited.
Thanks a lot.
--
Robert M. Münch
http://www.saphirion.com
smarter | better | faster
Re: CTFE template predicates
On Sunday, 3 May 2015 at 21:46:11 UTC, Robert M. Münch wrote:
Hi, I have now played a around couple of hours (reading
everything I could find) to get something to work, but I think
I'm missing some basic concepts/understanding. Maybe someone
can enlighten me how these things work. I thought that some
code from David Nadlinger is what I'm searching for but don't
know how to exactly make use of it.
Here is the code: I want to filter out some of the allMembers
and use them in my code for a switch/final to check that call
cases that were not filtered are covered. Trying to build the
enum for the switch/final statement.
auto org_rules = TypeTuple!(__traits(allMembers,BolSource));
static assert(!isTypeTuple!(org_rules));
template startsNotWith(T,char C){
static if (T[0] != C){
enum startsNotWith = true;
} else {
enum startsNotWith = false;
}
}
Here T would have to be a type. But you want to accept a string.
So:
template startsNotWith(string s,char c){
enum startsNotWith = s.length == 0 || s[0] != c;
}
template StaticFilter(alias pred, T...) {
static if (T.length == 0) {
alias TypeTuple!() StaticFilter;
} else static if (pred!(T[0])) {
alias TypeTuple!(T[0], StaticFilter!(pred, T[1 .. $]))
StaticFilter;
} else {
alias StaticFilter!(pred, T[1 .. $]) StaticFilter;
}
}
alias startsNotWithp = startsNotWith!(T,p); // doesn't
compile: Error: undefined identifier T
You need to turn T into a parameter, so that StaticFilter can set
it. (And it's really a string again, so I'm renaming to s.)
template startsNotWithp(string s)
{
enum startsNotWithp = startsNotWith!(s, 'p');
}
/* Shorthand syntax: enum startsNotWithp(string s) =
startsNotWith!(s, 'p'); */
alias rules = StaticFilter!(startsNotWithp, org_rules);
While playing with this a couple of questions came up:
1. How do predicates get their argument(s)? I saw code where
only the predicate was mentioned but no arguments. So, I assume
there is some behind-the-curtain-magic going on. I read about
things like a == b where I can reference 'a and 'b in a
string.
Predicates are called/instantiated by the thing to which you pass
them. StaticFilter instantiates pred for each element of the T
tuple it's given. If some documentation doesn't say how the
predicate will be called/instantiated, then it's probably assumed
to be obvious.
String predicates are turned into functions behind the curtains.
The thing you instantiate with a == b turns it into `(a, b)
{return a == b;}` and uses that. I think we don't do string
predicates for templates like StaticFilter, though.
2. enum startsNotwith = false So this is the return syntax
for a CTFE for return(true) ?
It's the template syntax for return false. CTFE does normal
functions at compile time, so there it's just return false.
/* Template: */
template t() {enum t = false;}
enum x = t!();
/* CTFE: */
bool f() {return false;}
enum y = f();
3. TupleType is a very missleading name when you are learning
these things, because the tuple can hold values as well.
Yup. And std.traits.isTypeTuple only adds to the confusion.
Or is there a more extensive explanation for the name I don't
get?
Not that I'm aware of.
4. Are there any tutorials about CTFE? This seems to be a very
powerful but not so easy to use feature of D, but documentation
is quite limited.
CTFE is rather simple. It just allows you to use certain
functions in a static (i.e. compile time) context.
Templates are more tricky. If you mean templates, maybe having
the right name helps.
Re: CTFE template predicates
On Sunday, 3 May 2015 at 21:46:11 UTC, Robert M. Münch wrote: 3. TupleType is a very missleading name when you are learning these things, because the tuple can hold values as well. Or is there a more extensive explanation for the name I don't get? Legacy we are trying to get rid of. See also: https://github.com/D-Programming-Language/phobos/pull/3128 https://github.com/D-Programming-Language/dlang.org/pull/986
Re: CTFE template predicates
On 4/05/2015 9:46 a.m., Robert M. Münch wrote:
Hi, I have now played a around couple of hours (reading everything I
could find) to get something to work, but I think I'm missing some basic
concepts/understanding. Maybe someone can enlighten me how these things
work. I thought that some code from David Nadlinger is what I'm
searching for but don't know how to exactly make use of it.
Here is the code: I want to filter out some of the allMembers and use
them in my code for a switch/final to check that call cases that were
not filtered are covered. Trying to build the enum for the switch/final
statement.
auto org_rules = TypeTuple!(__traits(allMembers,BolSource));
static assert(!isTypeTuple!(org_rules));
template startsNotWith(T,char C){
static if (T[0] != C){
enum startsNotWith = true;
} else {
enum startsNotWith = false;
}
}
template StaticFilter(alias pred, T...) {
static if (T.length == 0) {
alias TypeTuple!() StaticFilter;
} else static if (pred!(T[0])) {
alias TypeTuple!(T[0], StaticFilter!(pred, T[1 .. $])) StaticFilter;
} else {
alias StaticFilter!(pred, T[1 .. $]) StaticFilter;
}
}
alias startsNotWithp = startsNotWith!(T,p); // doesn't compile: Error:
undefined identifier T
alias rules = StaticFilter!(startsNotWithp, org_rules);
While playing with this a couple of questions came up:
1. How do predicates get their argument(s)? I saw code where only the
predicate was mentioned but no arguments. So, I assume there is some
behind-the-curtain-magic going on. I read about things like a == b
where I can reference 'a and 'b in a string.
2. enum startsNotwith = false So this is the return syntax for a CTFE
for return(true) ?
3. TupleType is a very missleading name when you are learning these
things, because the tuple can hold values as well. Or is there a more
extensive explanation for the name I don't get?
4. Are there any tutorials about CTFE? This seems to be a very powerful
but not so easy to use feature of D, but documentation is quite limited.
Thanks a lot.
Have you looked at my book? https://leanpub.com/ctfe
