why use string for this example of appender?

[Ali Çehreli]

On 04/15/2018 11:46 PM, WhatMeForget wrote:
 >
 > I think I got a handle on D's static and dynamic arrays, till I come to
 > std.array and see all the shiny new tools. I can understand all the
 > replace.. functions, but the appender function gave me pause. The
 > documentation says appender "Returns a new Appender or RefAppender
 > initialized with a given array."

New Appender allocates new memory. If an array is already available for 
an Appender to use, then it's more efficient.

 > My first thought that doesn't D's built in arrays already allow
 > appending? (at least for dynamic arrays)

Yes but Appender is reported to be faster presumably it uses a different 
allocation scheme and may be more free compared to dynamic arrays that 
must play well with GC and its pages.

 > And the example shows the use
 > of appender with string.  Isn't string an immutable array or
 > characters?

Mutable array of immutable characters: immutable(char)[].

What is important is that existing elements shoould not mutate so that 
existing slices don't get confused. Appending is fine because a new 
array is allocated and copied for the appending slice. (Aha! This 
feature is likely why Appender is faster than a dynamic array: it does 
not have the feature of "element stomping prevention". (Something is 
wrong with my English at the moment. :p))

 > Wouldn't this be the last data type you would want to be
 > appending to?

It's not unusual.

 > Another thing that had me wondering is the use of put()
 > down below; doesn't the append syntax (~=) give you the same exact
 > functionality; so why bother?

put() is old, ~= is new. Both are supported.

Ali