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    <p>Having constructors and destructors in my opinion is good, but not to do too much work in them. Especially not file/database access unless its very very specific to the class. You want to keep your constructors/destructors light to keep your program feeling fluid. Sometimes like already you have come to a case where the constructor does essentially all the work. There is a way to make things lighter. The concept/paradigm is called lazy evaluation. The idea is to accept inputs and do nothing (e.g. in constructor) but make use of the inputs when you need a calculation requested.</p> <p>Example: Lets say you have a class that reads a file, parses it and tells you info like the sum of all numbers in the file. You can do this all in the constructor. Using lazy evaluation you will merely open the file, and have a getTotalSum() function. When called it will do the parsing and give you the result. This way you can also have getBestFit() to get best fit line. Sometimes you dont want to get best fit and for some inputs you do. This way the user will not be waiting for the constructor to do the calculations before the user decides what to do. </p> <p>another example: lets say you have a view that loads 20 images. But only 5 are shown, and the constructor takes an array of the images to show. You can load them all in the constructor, but from a users perspective this will feel slow at the beginning. Or you can load 1 "loading" picture and load 1 image at a time. And as the user scrolls load more of the images on a as shown/needed basis.</p> <p>Of course 1 problem is that you find out of errors like invalid pictures later down the road instead of the constructor. You can always perform simple checks for yourself to pre-validate the input to some degree (e.g. check for correct password).</p>
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