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September 18, 2007
Clean my plate, but keep my wine bottle. (PHP; Static)
On Monday morning, I served Colin's breakfast on a clean plate in the "Whitworth" ... one happy camper, judging by the crumbs and butter wrappers left on the plate, and the smile on Colin's face.
Never wanting to disturb a customer's property and space, I carefully preserved the plate as Colin left it on that morning and returned the plate to him, in that same crumby condition, on Tuesday morning. But Colin didn't appreciate the care I had taken to preserve his crumbs and would have much preferred a clean start.
On Wednesday, I'll make sure he has a clean, pristine new plate!
When you call a function in PHP, the internal variables within that function are freshly re-initialised each time. There is no debris left over from previous operations. And that's a good and sensible default - just like Colin on Tuesday and Wednesday morning, you don't want to be reminded about what happened on Monday.
Colin drank a glass of wine out of a bottle he brought with him on Tuesday night, and came looking for it to have another glass on Wednesday night. He was a little unhappy that we had cleaned up and thrown out his undrunk wine, even though he had requested a clean breakfast plate each morning. This is an exception to the "clean up fully every time" rule ... and in PHP terms, you would declare a variable within the function to be static to ensure that its value is held from one call to the next.
Posted by gje at September 18, 2007 11:21 AM