Can we do compile time reading part of a file using import?

Steven Schveighoffer schveiguy at
Mon Oct 26 13:34:29 UTC 2020

On 10/23/20 12:42 PM, data pulverizer wrote:
> Hi all,
> the `import` function allows a file to be read at compile time, which 
> opens up great opportunities for (mostly binary) file IO, where data 
> types can be coded into files - the user doesn't need to know data types 
> ahead of time. As specified in my old blog article: 
> Binary files can be very large and reading the whole file at compile 
> time is often unnecessary.
> This isn't exactly the intended use for the function, but there it is. 
> Since compile time read capability already exists and is useful, adding 
> capability to be able to read only a portion of the file at compile time 
> in a given location is advantageous and has utility.
> For me it's not make-or-break, it just something very useful and I think 
> has clear use case. Please let me know if there are aspects or 
> alternatives I am missing.

I see no reason why the compiler can't do something special with:

enum slicedFile = import("foo.bin")[0 .. 100];

One thing that comes to mind -- most OSes support memory-mapped files. 
If import simply did a memory mapped file internally, and duplicated the 
string once actually used somewhere, then you can avoid full reading of 
the data until it's necessary.


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