[Issue 5491] filter cannot be used in a function?

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=5491


bearophile_hugs at eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs at eml.cc


--- Comment #5 from bearophile_hugs at eml.cc 2011-01-26 11:37:32 PST ---
(In reply to comment #0)

> import std.algorithm, std.conv, std.stdio;
> 
> enum UsbDevType: uint { indifferent = 0, parent_of_checked = 1, hub_dub_7 =
> 0x2001f103, spider_hub = 0x05e30608, gateway = 0x11A03232 }
> struct UsbDevice { //{{{ 
>     UsbDevType dev_type;
>     // not essential here ...
>     string toString(){ return to!string( dev_type ); }
> }
> 
> UsbDevice [] gateways_only( UsbDevice []devices ){ return filter!("a.dev_type
> == UsbDevType.gateway" )( devices ); }

This works:

auto gateways_only(UsbDevice[] devices) {
    return filter!((a){ return a.dev_type == UsbDevType.gateway; })(devices);
}(In reply to comment #0)
> The following code:
> _______________________________________________________________________________
> import std.algorithm, std.conv, std.stdio;
> 
> enum UsbDevType: uint { indifferent = 0, parent_of_checked = 1, hub_dub_7 =
> 0x2001f103, spider_hub = 0x05e30608, gateway = 0x11A03232 }
> struct UsbDevice { //{{{ 
>     UsbDevType dev_type;
>     // not essential here ...
>     string toString(){ return to!string( dev_type ); }
> }
> 
> UsbDevice [] gateways_only( UsbDevice []devices ){ return filter!("a.dev_type
> == UsbDevType.gateway" )( devices ); }
> 
> unittest{
>     auto devices  = [ UsbDevice( UsbDevType.gateway ), UsbDevice(
> UsbDevType.indifferent ), UsbDevice( UsbDevType.hub_dub_7 ) ];
>     auto gateways = gateways_only( devices );
>     foreach( UsbDevice dev; gateways ) writeln( dev.toString() );
> }

The formatting of your code is very bad.
This works:


import std.algorithm, std.conv, std.stdio;

enum UsbDevType: uint {
    indifferent = 0,
    parent_of_checked = 1,
    hub_dub_7 = 0x2001f103,
    spider_hub = 0x05e30608,
    gateway = 0x11A03232
}

struct UsbDevice {
    UsbDevType dev_type;

    string toString() {
        return to!string(dev_type);
    }
}

auto gateways_only(UsbDevice[] devices) {
    return filter!((a){ return a.dev_type == UsbDevType.gateway; })(devices);
}

void main() {
    auto devices = [UsbDevice(UsbDevType.gateway),
                    UsbDevice(UsbDevType.indifferent),
                    UsbDevice( UsbDevType.hub_dub_7)];

    auto gateways = gateways_only(devices);
    foreach (UsbDevice dev; gateways)
        writeln(dev.toString());
}


Currently string-defined functions that you give to filter, map, etc, can't use
symbol names defined elsewhere, like UsbDevType. So you need to use a lambda
template, as I have done here, or a proper delegate.

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------