dynamic get from variantArray() data table
data pulverizer via Digitalmars-d-learn
digitalmars-d-learn at puremagic.com
Tue Oct 13 09:22:34 PDT 2015
Thanks for the suggestion Alex, however I need the dynamic
behaviour properties of variantArray(), writing a struct each
time would be undesirable.
Perhaps I could boil down the question to something like, is
there a way of writing
auto x = dt[0][0];
auto y = x.get!(x.type - or whatever); // to get the actual value
of x rather than .VariantN! ... type
For some kind of auto cast back to basic type.
On Tuesday, 13 October 2015 at 15:51:40 UTC, Alex Parrill wrote:
> On Tuesday, 13 October 2015 at 15:17:15 UTC, data pulverizer
> wrote:
>> Hi,
>>
>> I am trying to use variantArray() as a data table object to
>> hold columns each of which is an array of a specific type. I
>> need to be able to get values from data table but I am having
>> problems ...
>>
>>
>> import std.stdio; // i/o
>> import std.variant; // type variations
>>
>> void main(){
>> // Columns of the table
>> string[] names = ["walter", "paul", "jeff", "andrie"];
>> int[] age = [55, 62, 27, 52];
>> string[] language = ["D", "Haskell", "Julia", "D"];
>> Variant[] dt = variantArray(names, age, language);
>>
>> foreach(col; dt){
>> foreach(el; col){
>> // here I try a kind of dynamic cast operator
>> auto x = el.get!(type(el)); // gives error
>> write(x);
>> }
>> write("\n");
>> }
>> }
>>
>> data_table.d(37): Error: cannot infer type for el
>> data_table.d(38): Error: undefined identifier 'el'
>>
>> Help
>>
>> DP
>
> You're trying to iterate over a `Variant`, which isn't
> implemented.
>
> You don't want to use a variant here anyway; you should use a
> struct or tuple for each entry in the table.
>
>
>
> import std.typecons;
>
> alias Entry = Tuple!(string, int, string);
>
> void main() {
> auto table = [Entry("walter", 55, "D"), Entry("paul", 62,
> "Haskell"), ... ]; // complete array
> foreach(entry; table) {
> writeln(entry.expand);
> }
> }
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