Assignment and copying

Put down a number, a text or another variable's contents — and how a copy differs from the original

easyYou need: Variables and names, Number, object and text

set is the first instruction almost every program puts down: before anything can be computed, the starting numbers have to come from somewhere.

Press “step” four times and watch the table.

steptick 0

Set0

=

Set1

=

Set2

=

Set3

=

@counter0number

stocknullnull

textnullnull

copynullnull

What can be put in

A number is written as it is: 5, -0.25, 1e6. A point, not a comma; the minus sign sits against the number.

Text goes in double quotes: "copper". In the variables table its type is string, and not every instruction works with it: text cannot be added to a number, but it can be printed.

A taken name — @copper, @this, @time. These are the game’s constants, and they are the next lesson.

Another variable — then the value is copied. More on that below.

Note

The second field accepts both a variable’s name and a value — the block does not care. That is exactly why a typo in a name is not an error: set copy stok simply copies emptiness.

A copy does not follow the original

The example’s third line is set copy stock, and at that moment stock holds a five. The fourth changes stock to 99, and copy stays a five.

That is the main rule: the value is copied, not a link. mlog has no “reference to a variable” and no way to say “let this variable always equal that one”. Every set line is a one-off action: take what is on the right now and put it on the left.

Silent failure

Hence a common mistake: copy a value once and expect it to keep updating. If copy has to follow stock, the line set copy stock has to run again and again — which the program does anyway if the line sits in the main loop.

And if there is an object on the right

A value is not always a number. If a variable holds a building or an item, that is what gets copied: set other container1 puts that very same container into other.

It does not make a copy of the container — there is one container, it is just that two variables now look at it. As with a number, copying is a one-off: demolish the container and both variables keep a building that no longer exists.

What set cannot do

• Compute. set total stock + 1 cannot be written: addition is op.
• Write into taken names. set @copper 7 does nothing. The one exception is @counter, where writing means a jump.
• Declare a variable in advance. mlog has no “declare a variable” line: a variable appears from its first mention, and set is simply the first place that usually happens.

Remember

• set puts a number, a text, a game constant or another variable’s value into a variable.
• The value is copied, not a link: after the copy the original can change freely.
• Copying is a one-off — for the value to keep up, the line has to run again.
• A building or an item is copied the same way: both names look at the same object.
• set has no calculations at all; op is for those.

Task

Swap the example’s third and fourth lines and run the iteration again: now copy becomes 99, because what is copied is whatever the variable holds at the moment the line runs.

Then type text instead of "copper" in the second line — with no quotes. That is no longer text but a variable’s name: the field accepts it, the program does not break, and text ends up holding emptiness, because nobody ever put anything into a variable by that name.