Is there an opposite of .toString()?

[Faux Amis]

On 2017-10-14 05:47, Jonathan M Davis wrote:
> On Saturday, October 14, 2017 00:18:35 myst via Digitalmars-d-learn wrote:
>> I'm sorry if this has been answered already, it seems like a very
>> basic question.
>>
>> There is .toString() method convention for printing, but I can
>> not find anything alike for reading. Is there something like
>> operator>>() in C++? What's an ideomatic way of reading an object?
> 
> The function to use for conversions in general is std.conv.to. And really,
> there isn't much of a reason to ever call toString. Functions like writeln,
> format, and to may use it internally, but it's more or less an anti-pattern
> to do so in your own code - especially if we're talking about generic code.
> If you're looking to convert something to string, to!string works with
> pretty much everything and toString works with considerably less. And if
> there's a generic way to convert from string to something else, it's also
> with to - e.g. to!int("42"). However, for that conversion to work, it either
> has to be a built-in type so that to understands it, or the type will need a
> constructor that takes a string. In general, in order to generically convert
> to a user-defined type, either that target type must have a constructor that
> accepts that source type, or the source type must define opCast or an alias
> to convert to the target type. std.conv.to is very powerful, but it does
> need to have something to work with. If anything approaching a standard
> conversion exists, it can be done with std.conv.to; otherwise, it's going to
> depend on the type.
> 
> I think that in general, you're going to find that converting to a string
> works with most everything, but aside from built-in types, converting from a
> string with std.conv.to is unlikely to work. _Some_ types do have
> constructors that take strings, but most don't. Built-in types will work,
> because std.conv.to understands how to do that conversion. For user-defined
> types, either you're likely going to have to parse the string yourself, or
> they may contain another function for doing the conversion (for instance
> std.datetime.systime.SysTime uses toISOExtString and fromISOExtString to
> convert to and from the ISO extended format for a date and time and has
> other functions for other time formats).
> 
> You can also check out std.conv.parse, which acts similarly to std.conv.to,
> but whereas to converts the entire string, parse converts the first portion
> of a string and therefore is meant to allow for parsing multiple values from
> a string.
> 
> - Jonathan M Davis
> 
Thanks for the proper/complete reply ;)