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digitalmars.D.announce - lookuptable

reply Steven Schveighoffer <schveiguy gmail.com> writes:
Just wanted to throw this out there on a slow day. I wrote this little 
utility to generate static lookup tables, because using an AA is too 
expensive for something like e.g. looking up database row data by column 
name.

It's very crude, but very short and sweet. Hopefully people find a use 
for it.

Let me know if you have any requests or find any bugs on github.

https://code.dlang.org/packages/lookuptable

-Steve
Apr 22 2020
parent reply Sebastiaan Koppe <mail skoppe.eu> writes:
On Wednesday, 22 April 2020 at 20:27:12 UTC, Steven Schveighoffer 
wrote:

 Just wanted to throw this out there on a slow day. I wrote this 
 little utility to generate static lookup tables, because using 
 an AA is too expensive for something like e.g. looking up 
 database row data by column name.

 It's very crude, but very short and sweet. Hopefully people 
 find a use for it.

 Let me know if you have any requests or find any bugs on github.

 https://code.dlang.org/packages/lookuptable

 -Steve


Nice.

For the indexLookup you can also use 
https://github.com/skoppe/perfect-hash
Apr 22 2020
next sibling parent Sebastiaan Koppe <mail skoppe.eu> writes:
On Wednesday, 22 April 2020 at 21:21:31 UTC, Sebastiaan Koppe 
wrote:

 For the indexLookup you can also use 
 https://github.com/skoppe/perfect-hash


That is not quite true, only for strings.
Apr 22 2020
prev sibling parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 4/22/20 5:21 PM, Sebastiaan Koppe wrote:

 On Wednesday, 22 April 2020 at 20:27:12 UTC, Steven Schveighoffer wrote:

 Just wanted to throw this out there on a slow day. I wrote this little 
 utility to generate static lookup tables, because using an AA is too 
 expensive for something like e.g. looking up database row data by 
 column name.

 It's very crude, but very short and sweet. Hopefully people find a use 
 for it.

 Let me know if you have any requests or find any bugs on github.

 https://code.dlang.org/packages/lookuptable


 
 Nice.
 
 For the indexLookup you can also use https://github.com/skoppe/perfect-hash


Hm... thanks for the suggestion. I'm not sure if it fits here, as the 
point is to avoid runtime cost and GC allocation, not make lookups 
uber-fast.

These are meant to be short-lived things. My main target was e.g. 
mysql-native has an "asAA" function which generates an AA with keys 
being the column names. This is kind of crappy, because if you do that 
for each row, then you are generating and throwing away a LOT of data.

But if you generate the lookup index once per sequence, and you reuse 
that, you have much more efficiency, and are only generating one array. 
Possibly if I can figure out a good API, you could do it with 
malloc/free instead of using GC, but I'm happy with it right now anyway.

-Steve
Apr 22 2020
parent Sebastiaan Koppe <mail skoppe.eu> writes:
On Thursday, 23 April 2020 at 04:29:12 UTC, Steven Schveighoffer 
wrote:

 Hm... thanks for the suggestion. I'm not sure if it fits here, 
 as the point is to avoid runtime cost and GC allocation, not 
 make lookups uber-fast.


Granted, it was far-fetched.


 These are meant to be short-lived things. My main target was 
 e.g. mysql-native has an "asAA" function which generates an AA 
 with keys being the column names. This is kind of crappy, 
 because if you do that for each row, then you are generating 
 and throwing away a LOT of data.


Yeah, that is quite crappy. I remember mapping each row to a 
struct and use member access, but then you have to sync the 
struct and the query yourself.

It doesn't have to be short-lived though. Most apps process the 
same set of queries, so pre-creating all your prepared statements 
and mappings might make sense. I am not sure about mysql, but 
postgres gives you back the columns and types after preparing a 
statement, so you could do some runtime mapping once at startup 
(and at each reconnect).
Apr 23 2020