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.


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