digitalmars.D.learn - CTFE & template predicates
- =?iso-8859-1?Q?Robert_M._M=FCnch?= (47/47) May 03 2015 Hi, I have now played a around couple of hours (reading everything I
- anonymous (43/90) May 03 2015 Here T would have to be a type. But you want to accept a string.
- =?iso-8859-1?Q?Robert_M._M=FCnch?= (12/31) May 04 2015 Hi, ok, just to better understand this (I have a C++ background (even
- anonymous (21/26) May 04 2015 In template parameter lists, a solitary identifier is a type
- =?iso-8859-1?Q?Robert_M._M=FCnch?= (8/20) May 04 2015 Hi, I have one more questions: Is it possible to write something like th...
- anonymous (2/6) May 04 2015 No, we don't have template literals.
- "Per =?UTF-8?B?Tm9yZGzDtnci?= <per.nordlow gmail.com> (3/6) May 06 2015 Better still:
- Dicebot (4/7) May 03 2015 Legacy we are trying to get rid of. See also:
- Rikki Cattermole (2/45) May 03 2015 Have you looked at my book? https://leanpub.com/ctfe
- =?iso-8859-1?Q?Robert_M._M=FCnch?= (6/7) May 04 2015 No, thanks for the hint. You will have one more reader ;-)
- Rikki Cattermole (3/6) May 04 2015 I'm currently live streaming, feel free to jump on and ask any questions...
- =?iso-8859-1?Q?Robert_M._M=FCnch?= (9/10) May 04 2015 I bought it. Will it be updated?
- Rikki Cattermole (4/10) May 04 2015 It's due for an update.
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
May 03 2015
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 TYou 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.
May 03 2015
On 2015-05-03 23:28:00 +0000, 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.Well, and often it's obvious that it's not obvious ;-)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.Ok, that helps to better understand how this works. Thanks for the feedback. -- Robert M. Münch http://www.saphirion.com smarter | better | faster
May 04 2015
"anonymous" <anonymous example.com> 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. */ } ----
May 04 2015
On 2015-05-03 23:28:00 +0000, 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
May 04 2015
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.
May 04 2015
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; }
May 06 2015
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
May 03 2015
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
May 03 2015
On 2015-05-04 03:52:21 +0000, Rikki Cattermole said:Have you looked at my book? https://leanpub.com/ctfeNo, thanks for the hint. You will have one more reader ;-) -- Robert M. Münch http://www.saphirion.com smarter | better | faster
May 04 2015
On 4/05/2015 11:15 p.m., Robert M. Münch wrote:On 2015-05-04 03:52:21 +0000, Rikki Cattermole said:I'm currently live streaming, feel free to jump on and ask any questions! https://www.livecoding.tv/alphaglosined/Have you looked at my book? https://leanpub.com/ctfeNo, thanks for the hint. You will have one more reader ;-)
May 04 2015
On 2015-05-04 03:52:21 +0000, Rikki Cattermole said:Have you looked at my book? https://leanpub.com/ctfeI 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
May 04 2015
On 5/05/2015 6:24 a.m., Robert M. Münch wrote:On 2015-05-04 03:52:21 +0000, Rikki Cattermole said:It's due for an update. Basically I just need to be told what people want. Otherwise I'll be doing it blind!Have you looked at my book? https://leanpub.com/ctfeI 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.
May 04 2015