fixes #375 integer types are error prone

This change converts the various integer types like nng_socket
in the public API to opaque structures that are passed by value.
Basically we just wrap the integer ID.  This "hack" give us strong
type checks by the compiler (yay!), at the expense of not being able
to directly use these as numbers (so comparisions for example don't
work, and neither does initialization to zero using the normal
method.

Comparison of disassembly output shows that at least with the optimizer
enabled there is no difference in the compiler output between using
a structure or an integral value.

1 files changed, 8 insertions, 3 deletions

diff --git a/docs/man/nng_dialer.5.adoc b/docs/man/nng_dialer.5.adoc
index daadbd0b..45c60bc9 100644
--- a/docs/man/nng_dialer.5.adoc
+++ b/docs/man/nng_dialer.5.adoc
@@ -16,11 +16,11 @@ nng_dialer - dialer
 == SYNOPSIS
 
 [source, c]
------------
+----
 #include <nng/nng.h>
 
-typedef uint32_t nng_dialer;
------------
+typedef struct nng_dialer_s nng_dialer;
+----
 
 == DESCRIPTION
 
@@ -38,6 +38,11 @@ Dialer objects are created by the
 or <<nng_dial.3#,`nng_dial()`>> functions, and are always "`owned`"
 by a single <<nng_socket.5#,`nng_socket`>>.
 
+IMPORTANT: The `nng_dialer` structure is always passed by value (both
+for input parameters and return values), and should be treated opaquely.
+Passing structures this way ensures gives the compiler a chance to perform
+accurate type checks in functions passing values of this type.
+
 TIP: A given <<nng_socket.5#,`nng_socket`>> may have multiple dialer
 objects, multiple <<nng_listener.5#,listener>> objects, or even some
 of both.