digitalmars.D.learn - Opinions on iterating a struct to absorb the decoding of a CSV?
- Andy Valencia (27/27) Mar 28 I wanted a lightweight and simpler CSV decoder. I won't post the
- H. S. Teoh (9/24) Mar 28 This is pretty clean, and is a good example of DbI. I use the same
- cc (117/119) Mar 31 That's pretty much the best way to do it. While `.tupleof` does
- cc (6/11) Mar 31 Turns out this can be done as part of the panacea that is `is()`
I wanted a lightweight and simpler CSV decoder. I won't post the
whole thing, but basically you instantiate one as:
struct Whatever {
...
}
...
f = File("path.csv", "r");
auto c = CSVreader!Whatever(f);
foreach (rec; c) { ...
CSVreader is, of course, templated:
struct CSVreader(T) {
...
}
and the innermost bit of CSVreader is:
auto t = T();
foreach (i, ref val; t.tupleof) {
static if (is(typeof(val) == int)) {
val = this.get_int();
} else {
val = this.get_str();
}
}
return t;
So you cue off the type of the struct field, and decode the next
CSV field, and put the value into the new struct.
Is there a cleaner way to do this? This _does_ work, and gives
me very compact code.
Mar 28
"H. S. Teoh" <hsteoh qfbox.info>
On Thu, Mar 28, 2024 at 05:23:39PM +0000, Andy Valencia via Digitalmars-d-learn
wrote:
[...]
auto t = T();
foreach (i, ref val; t.tupleof) {
static if (is(typeof(val) == int)) {
val = this.get_int();
} else {
val = this.get_str();
}
}
return t;
So you cue off the type of the struct field, and decode the next CSV
field, and put the value into the new struct.
Is there a cleaner way to do this? This _does_ work, and gives me
very compact code.
This is pretty clean, and is a good example of DbI. I use the same
method in my fastcsv experimental module to transcribe csv to an array
of structs:
https://github.com/quickfur/fastcsv
T
--
Today's society is one of specialization: as you grow, you learn more and more
about less and less. Eventually, you know everything about nothing.
Mar 28
On Thursday, 28 March 2024 at 17:23:39 UTC, Andy Valencia wrote:I wanted a lightweight and simpler CSV decoder. I won't post the whole thing, but basically you instantiate one as:That's pretty much the best way to do it. While `.tupleof` does look kind of hacky, and you could instead iterate using `___traits(allMembers, T)` and `__traits(getMember, T, "symbolname")` which looks more self-documenting, this ends up being more of a pain, because it's going to iterate through everything in the type, including functions, constructors/destructors, aliases, enums, static members, inherited members in classes, etc etc, and it's a plate of spaghetti to sort them all out, plus there are issues with aliasing on top of that. Sometimes you might want to do that of course, but for simple situations like this, `.tupleof` just works. ```d struct Foo { int x = 1; float f = 3.14; string abc = "abc"; string[] xyz; immutable int i; const int c; this(int x) { this.x = x; i = 7; c = 8; } this(float f) { this.f = f; } bool speak() { return false; } bool speak(bool b) { return b; } void toString(scope void delegate(const(char)[]) writer) { /*...*/ } alias X = int; enum E = 3; static enum F = 4; static int y = 5; } void main() { Foo foo; dumpInfo(foo); } void dumpInfo(T)(T t) { import std.traits; static foreach (idx, field; T.tupleof) {{ alias TYPE = typeof(field); enum NAME = field.stringof; writefln("[%s] %s => %s", TYPE.stringof, NAME, t.tupleof[idx]); }} writeln; static foreach (sym; __traits(allMembers, T)) {{ enum bool ISSTATIC = hasStaticMember!(T, sym); static if (ISSTATIC) alias SYM = __traits(getMember, T, sym); else alias SYM = __traits(getMember, t, sym); enum NAME = sym; static if (isType!SYM) { // aliases writefln("(TYPE) %s : %s", NAME, SYM.stringof); } else static if (isFunction!SYM) { alias OVERLOADS = __traits(getOverloads, T, sym); static foreach (idx, FUNC; OVERLOADS) { writefln("(FUNC) %s<%s> : %s", NAME, idx, typeof(FUNC).stringof); writefln("\t%s %s %s", ReturnType!FUNC.stringof, Parameters!FUNC.stringof, ParameterIdentifierTuple!FUNC.stringof); // Useful } } else { alias TYPE = typeof(SYM); // where is isEnum or isManifestConstant? enum bool ISASSIGNABLE = __traits(compiles, {__traits(getMember, t, sym) = __traits(getMember, t, sym);}); enum bool ISASSIGNABLE_IN_CTOR = __traits(compiles, {cast()__traits(getMember, t, sym) = cast()__traits(getMember, t, sym);}); static if (!ISASSIGNABLE && !ISASSIGNABLE_IN_CTOR) { // MAYBE it's an enum. Or something else unassignable. writefln("(ENUM) [%s] %s => %s", TYPE.stringof, NAME, SYM); } else static if (ISSTATIC) { writefln("(STATIC) [%s] %s => %s", TYPE.stringof, NAME, SYM); } else { writefln("[%s] %s => %s", TYPE.stringof, NAME, __traits(getMember, t, sym)); // SYM doesn't work here } } }} } ``` ``` [int] x => 1 [float] f => 3.14 [string] abc => abc [string[]] xyz => [] [immutable(int)] i => 0 [const(int)] c => 0 [int] x => 1 [float] f => 3.14 [string] abc => abc [string[]] xyz => [] [immutable(int)] i => 0 [const(int)] c => 0 (FUNC) __ctor<0> : ref Foo(int x) Foo (int) AliasSeq!("x") (FUNC) __ctor<1> : ref Foo(float f) Foo (float) AliasSeq!("f") (FUNC) speak<0> : bool() bool () () (FUNC) speak<1> : bool(bool b) bool (bool) AliasSeq!("b") (FUNC) toString<0> : void(scope void delegate(const(char)[]) writer) void (scope void delegate(const(char)[])) AliasSeq!("writer") (TYPE) X : int (ENUM) [int] E => 3 (ENUM) [int] F => 4 (STATIC) [int] y => 5 ``` I scoured [Traits](https://dlang.org/spec/traits.html) and [std.traits](https://dlang.org/phobos/std_traits.html) looking for a simple method to tell whether a member was declared as enum but couldn't find one, so if anyone knows a proper way to do it please let me know.
Mar 31
On Monday, 1 April 2024 at 04:54:46 UTC, cc wrote:I scoured [Traits](https://dlang.org/spec/traits.html) and [std.traits](https://dlang.org/phobos/std_traits.html) looking for a simple method to tell whether a member was declared as enum but couldn't find one, so if anyone knows a proper way to do it please let me know.Turns out this can be done as part of the panacea that is `is()` statements. ```d static if (is(typeof({enum X = SYM;}))) ```
Mar 31