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digitalmars.D.learn - What does dot before method name mean?

reply Stephen Miller <harakim gmail.com> writes:
I am writing a tcp proxy server and I noticed that when a socket 
is in non-blocking mode, it returns -1 if it doesn't receive 
data, as opposed to 0.
I wanted to track down the documentation or figure out what might 
be going on, so I went to the dlang documentation page for 
std.socket.Socket. The code for receive calls .recv. I don't know 
where that is defined. It calls other methods in the same way (eg 
.recvFrom).

Here is the actual code:
```d
return buf.length
                    ? .recv(sock, buf.ptr, capToInt(buf.length), 
cast(int) flags)
                    : 0;
```

This is the reference.
https://github.com/dlang/phobos/blob/19264401a8873c211b0ee815fef660d6e7eb081d/std/socket.d#L3085


My questions are: What does the dot in front of recv mean? Where 
is that code?
May 07 2021
parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Saturday, 8 May 2021 at 01:45:49 UTC, Stephen Miller wrote:

 I am writing a tcp proxy server and I noticed that when a 
 socket is in non-blocking mode, it returns -1 if it doesn't 
 receive data, as opposed to 0.


It sets the `wouldHaveBlocked` flag in that case returning -1. 0 
always means connection closed.


 My questions are: What does the dot in front of recv mean? 
 Where is that code?


Leading dot means to look it up from top level instead of the 
local/class member. So then it uses the system function - recv 
from C - instead of the local ones.
May 07 2021
parent reply Stephen Miller <harakim gmail.com> writes:
On Saturday, 8 May 2021 at 01:48:22 UTC, Adam D. Ruppe wrote:

 On Saturday, 8 May 2021 at 01:45:49 UTC, Stephen Miller wrote:

 I am writing a tcp proxy server and I noticed that when a 
 socket is in non-blocking mode, it returns -1 if it doesn't 
 receive data, as opposed to 0.


 It sets the `wouldHaveBlocked` flag in that case returning -1. 
 0 always means connection closed.


 My questions are: What does the dot in front of recv mean? 
 Where is that code?


 Leading dot means to look it up from top level instead of the 
 local/class member. So then it uses the system function - recv 
 from C - instead of the local ones.


Thanks for the explanation. Is there an easy way to know what the 
system functions are? Is it defined by the standard library or 
does it just include all the system libraries (or some subset) 
for the operating system you are on?

Also, thanks for the wouldHaveBlocked flag information. That 
makes everything about the socket method return types make sense.
May 07 2021
parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Saturday, 8 May 2021 at 02:29:18 UTC, Stephen Miller wrote:

 Is there an easy way to know what the system functions are?


they are imported.

Windows uses winsock:
http://phobos.dpldocs.info/source/std.socket.d.html#L50

posix uses their socket thing:
http://phobos.dpldocs.info/source/std.socket.d.html#L80


So all the leading dot does is go back to the top level - the 
module - and then if there's a local one defined there, it uses 
it, otherwise it scans the imports like normal to find it.

See my search results:

http://dpldocs.info/recv

and you can see where the bindings come from.

So it binds to these functions ultimately:

https://man7.org/linux/man-pages/man2/recv.2.html

https://docs.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-recv
May 07 2021
parent Stephen Miller <harakim gmail.com> writes:
On Saturday, 8 May 2021 at 02:33:44 UTC, Adam D. Ruppe wrote:

 On Saturday, 8 May 2021 at 02:29:18 UTC, Stephen Miller wrote:

 Is there an easy way to know what the system functions are?


 they are imported.

 Windows uses winsock:
 http://phobos.dpldocs.info/source/std.socket.d.html#L50

 posix uses their socket thing:
 http://phobos.dpldocs.info/source/std.socket.d.html#L80


 So all the leading dot does is go back to the top level - the 
 module - and then if there's a local one defined there, it uses 
 it, otherwise it scans the imports like normal to find it.

 See my search results:

 http://dpldocs.info/recv

 and you can see where the bindings come from.

 So it binds to these functions ultimately:

 https://man7.org/linux/man-pages/man2/recv.2.html

 https://docs.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-recv


Thanks. Your answers are always great!
May 07 2021