Expression templates

So, imagine you have a bunch of toys: blocks, cars, legos, and you want to put them together in a tower. If you want to make a really tall tower, you might need to stack a lot of blocks on top of each other. And, let's say you want to put a car on top of the tower. But, you also want to make sure the car is red.

Now, you could go through all your toys, one by one, and pick out the red car. And then, you could stack all the blocks until you have a really tall tower. Finally, you could put the car on top of the tower.

But, what if there was a faster, simpler way to do this? What if the blocks, cars, and legos were "expressions" and you could use them to build your tower, without having to go through each toy individually?

That's kind of like what expression templates are. They allow you to use different pieces of code (which are the "expressions") and combine them together to make something new (like building the tower with the red car on top).

So, instead of having to go through each toy and telling the computer what to do with it, you can use expression templates to have the computer build the tower faster and more efficiently. It's like having a toy box full of Legos that can be combined in different ways to make different toys.

But, just like building with Legos, using expression templates can be a bit complex and require some advanced coding skills. So, it's not something that most 5-year-olds would be able to understand or use just yet.