Is there anyway to make this work?

Solar2D General Questions/Discussion
#1

Hi,

Apparently this is wrong:

myTable = {} myTable.value = myTable.value + 1  

Is there anyway to make this work? i.e. without initializing the “value” field first and have it initialized at zero by default.

Thanks.

#2

Any value that isn’t initialized is ‘nil’, which means it’s not a math object and cannot be used for math right off the bat. So instead you should do this:

[lua]myTable = {}

myTable.value = (myTable.value or 0) + 1[/lua]

#3

…or you could use a metatable. 

The metatable below will automatically set any uninitialized member to 0.

local myTable = {}; setmetatable(myTable, {     \_\_index = function(t, key)         return 0;     end }) myTable.value = myTable.value + 1   -- returns 1 myTable.value = myTable.value + 1   -- returns 2 myTable.otherValue = myTable.otherValue + 1   -- also returns 1
#4

Fantastic tip, and something that vets forget. 

#5

Any value that isn’t initialized is ‘nil’, which means it’s not a math object and cannot be used for math right off the bat. So instead you should do this:

[lua]myTable = {}

myTable.value = (myTable.value or 0) + 1[/lua]

#6

…or you could use a metatable. 

The metatable below will automatically set any uninitialized member to 0.

local myTable = {}; setmetatable(myTable, {     \_\_index = function(t, key)         return 0;     end }) myTable.value = myTable.value + 1   -- returns 1 myTable.value = myTable.value + 1   -- returns 2 myTable.otherValue = myTable.otherValue + 1   -- also returns 1
#7

Fantastic tip, and something that vets forget.