Tips on Lua syntax

Object reference variations

First, there are three object reference variations:

-- #1 module . submodule . name
tarantool> box.space.tester:select{1}
-- #2 replace name with a literal in square brackets
tarantool> box.space['tester']:select{1}
-- #3 use a variable for the entire object reference
tarantool> s = box.space.tester
tarantool> s:select{1}

Examples in this manual usually have the “box.space.tester:” form (#1). However, this is a matter of user preference and all the variations exist in the wild.

Also, descriptions in this manual use the syntax “space_object:” for references to objects which are spaces, and “index_object:” for references to objects which are indexes (for example box.space.tester.index.primary:).

Parameter variations

Then, there are seven parameter variations:

-- #1
tarantool> box.space.tester:select{1}
-- #2
tarantool> box.space.tester:select({1})
-- #3
tarantool> box.space.tester:select(1)
-- #4
tarantool> box.space.tester.select(box.space.tester,1)
-- #5
tarantool> box.space.tester:select({1},{iterator='EQ'})
-- #6
tarantool> variable = 1
tarantool> box.space.tester:select{variable}
-- #7
tarantool> variable = {1}
tarantool> box.space.tester:select(variable)

Lua allows to omit parentheses () when invoking a function if its only argument is a Lua table, and we use it sometimes in our examples. This is why select{1} is equivalent to select({1}). Literal values such as 1 (a scalar value) or {1} (a Lua table value) may be replaced by variable names, as in examples #6 and #7.

Although there are special cases where braces can be omitted, they are preferable because they signal “Lua table”. Examples and descriptions in this manual have the {1} form. However, this too is a matter of user preference and all the variations exist in the wild.

Rules for object names

Database objects have loose rules for names: the maximum length is 65000 bytes (not characters), and almost any legal Unicode character is allowed, including spaces, ideograms and punctuation.

In those cases, to prevent confusion with Lua operators and separators, object references should have the literal-in-square-brackets form (#2), or the variable form (#3). For example:

tarantool> box.space['1*A']:select{1}
tarantool> s = box.space['1*A !@$%^&*()_+12345678901234567890']
tarantool> s:select{1}

Disallowed:

• characters which are unassigned code points,
• line and paragraph separators,
• control characters,
• the replacement character (U+FFFD).

Not recommended: characters which cannot be displayed.

Names are “case sensitive”, so ‘A’ and ‘a’ are not the same.