[alexandria-devel] [PATCH] lazy-evaluate the default value in ENSURE-GETHASH

[Ryan Davis]

I'm using a hash-table as a cache, and had a problem with
ensure-gethash. Some example code / output:

CL-USER> (let ((h (make-hash-table)))
  (alexandria:ensure-gethash :x h (progn (format T "expensive
computation~%") 1))
  (alexandria:ensure-gethash :x h (progn (format T "expensive
computation~%") 1)))
expensive computation
expensive computation
1
T
CL-USER>

This patch (created using git format-patch origin/master) converts
ENSURE-GETHASH to a macro that only evaluates the default if we get to
the setf branch. Has a check to create and call a lambda if the default
value looks complicated (using CONSTANTP).

After applying my patch, here's the output:
CL-USER> (let ((h (make-hash-table)))
  (alexandria:ensure-gethash :x h (progn (format T "expensive
computation~%") 1))
  (alexandria:ensure-gethash :x h (progn (format T "expensive
computation~%") 1)))
expensive computation
1
T
CL-USER>

Thoughts?

Thanks,

-- 
Ryan Davis
Acceleration.net
Director of Programming Services
2831 NW 41st street, suite B
Gainesville, FL 32606

Office: 352-335-6500 x 124
Fax: 352-335-6506

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