Constructing localized strings in game

[Pi-C]

I've another localization problem.

Suppose you have these strings defined:

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[strings]
list=You get __1__ as result.
AND=and

That's easy to use if you only want to show one value:

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local a = "an iron gear"
game.print({"", "strings.list", a})

But how about a list composed of variables that may or may not be set?

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local a = entity.get_driver()
if a then a = a. player end
local b = entity.get_passenger()
if b then b = b.player end

local output = ""
if a then output = a end
if a and b then output = output .. ' ' .. {"strings.AND"} .. ' ' end
if b then output = output .. b

game.print({"", "strings.list", output})

I can't get this to work! The best I could achieve was getting wrong output (output would contain literal "strings.AND" instead of localized "and") without crashing the game, the worst was a crash due to trying to concatenate a table when a string was expected. Where is my mistake?

[DaveMcW]

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[strings]
list=You get __1__ as result.
AND=__1__ and __2__

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game.print({"strings.list", {"strings.AND", {"item-name.copper-plate"}, {"item-name.iron-plate"}}})

[Pi-C]

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[strings]
list=You get __1__ as result.
AND=__1__ and __2__

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game.print({"strings.list", {"strings.AND", {"item-name.copper-plate"}, {"item-name.iron-plate"}}})

That's so easy again … So, I don't have to add the individual pieces to compose one string, but define three different strings (one for "only a", one for "only b", one for "a and b" -- I can't use variables that have no value).

Guess it was getting too late last night, and switching between different Factorio instances (with occasional restarts of both because otherwise the mods' checksums would cause desync) so many times took its toll. Thank you for your help!

[eradicator]

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game.print({"", "strings.list", output})

Only the first string in each localised string (==table) is a template, so this would literally print "strings.list".

But so many possibilities to get to your result:

Dynamic composition:

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[strings]
youhave=You have __1__.
and=and

if driver and passenger then
  game.print{"strings.youhave",{"",driver,{"strings.and"},passenger}}
else
  game.print{"strings.youhave",driver or passenger}
  end

By-case templates:

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[strings]
twothing=You have __1__ and __2__
onething=You have __1__  
  
if driver and passenger then
  game.print{"strings.twothing",driver,passenger}
else
  game.print{"strings.onething",driver or passenger}
  end

I can"t use variables that have no value).

A localized string is a table, so you can abuse the fact that in lua every undefined element is nil, so adding nil to the end of a table does nothing:

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local lstring = {"","hi "}
local last_name = "foo"
local first_name = nil
table.insert(lstring,"my name is ")
table.insert(lstring,first_name)
table.insert(lstring,last_name)

[Pi-C]

But so many possibilities to get to your result:

Dynamic composition:

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if driver and passenger then
  game.print{"strings.youhave",{"",driver,{"strings.and"},passenger}}
else
  game.print{"strings.youhave",driver or passenger}
  end

I like this one! The "or" saves one ifelse-block, that's more elegant than my current solution.

By-case templates:

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[strings]
twothing=You have __1__ and __2__
onething=You have __1__  

Will definitely work, but means more strings to translate.

I can"t use variables that have no value).

A localized string is a table, so you can abuse the fact that in lua every undefined element is nil, so adding nil to the end of a table does nothing:

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local lstring = {"","hi "}
local last_name = "foo"
local first_name = nil
table.insert(lstring,"my name is ")
table.insert(lstring,first_name)
table.insert(lstring,last_name)

That's a neat trick! Basically, it's the same thing I tried to achieve (build the message from individual blocks if these blocks exist), but without any checks required, so it looks much cleaner. Thanks for showing!