Document dbg_macro::prettyPrint in README (if it's still there)

[alexeyr]

I found a Reddit comment saying

If you want to format the output specifically for dbg(), specialize dbg_macro::prettyPrint

If this is officially supported, can you add it to README? And if not, have some alternative?

[sharkdp]

This is still possible, but the name has changed. You can specialize dbg::pretty_print(std::ostream&, const T&). Here is the builtin example for char:

inline bool pretty_print(std::ostream& stream, const char& value) {
  const bool printable = value >= 0x20 && value <= 0x7E;

  if (printable) {
    stream << "'" << value << "'";
  } else {
    stream << "'\\x" << std::setw(2) << std::setfill('0') << std::hex
           << std::uppercase << (0xFF & value) << "'";
  }
  return true;
}

The Boolean return value determines whether or not the expression and the type name should be printed as well.

add it to README

Sounds good!

[alexeyr]

Actually does it need to be in namespace dbg or can ADL let you use pretty_print in your own namespace?

[sharkdp]

I haven't checked, but I'd be fine with a change to use ADL to enable non-dbg-namespace usage.

[winwinashwin]

Is there any reason one should prefer specializing pretty_print over operator<< for user defined datatypes? The latter seems already documented.

[sharkdp]

operator<< on ostream might already be implemented for some types (for other use cases.. with non-ideal output). specializing pretty_print might be needed in those cases. But yeah, I haven't seen any need for this so far, so I'm fine with closing this for now. @alexeyr please report back if you think this should still be resolved.

[alexeyr]

I don't need it currently. But the point would be to use it when you want different output than operator<<, similarly to Rust's Debug ("should format the output in a programmer-facing, debugging context" vs Display ("for user-facing output").

[alexeyr]

I don't actually remember why exactly I wanted it originally, I think for something like std::vector<our_type> where we wouldn't want to change the behavior everywhere.