On Friday, 18 August 2017 at 02:38:15 UTC, WhatMeForget wrote:
Can someone explain what is the difference between the two?
Thanks.
module gates;
import std.stdio;
import std.random;
alias Calculator = int delegate(int);
Calculator makeCalculator()
{
static int context = 0;
int randy = uniform(1, 7);
context++;
writeln("context = ", context);
writeln("randy = ", randy);
return value => context + randy + value;
}
void main()
{
for (int i = 0; i < 3; i++)
{
auto calculator = makeCalculator();
writeln("The result of the calculation: ",
calculator(0));
}
}
returns:
context = 1
randy = 5
The result of the calculation: 6
context = 2
randy = 2
The result of the calculation: 4
context = 3
randy = 6
The result of the calculation: 9
while the following
void main()
{
auto calculator = makeCalculator(); // thought just one
would work
for (int i = 0; i < 3; i++)
{
writeln("The result of the calculation: ",
calculator(0));
}
}
returns:
The result of the calculation: 3
The result of the calculation: 3
The result of the calculation: 3
This actually appears correct ...
The 1-st example:
Each call to makeCalculator() increments a static (i.e. shared
among all makeCalculator() instances) variable - context.
In addition, makeCalculator() generates a random variable.
Whereas the delegate merely captures these variables, and the
displayed results reflect this.
The 2-nd example:
There is a single call to makeCalculator().
After this call, context == 1, randy == _apparently 2_.
Now the delegate, as has already been said, merely captures these
values, so consecutive calls do not change the result.
