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Note in the manual about using '...' as an expression

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Roberto Ierusalimschy 2022-09-08 17:21:02 -03:00
parent cd56f222b7
commit 71bc69c2af
1 changed files with 16 additions and 5 deletions
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@ -1144,7 +1144,9 @@ Lua also accepts @x{hexadecimal constants},
which start with @T{0x} or @T{0X}. which start with @T{0x} or @T{0X}.
Hexadecimal constants also accept an optional fractional part Hexadecimal constants also accept an optional fractional part
plus an optional binary exponent, plus an optional binary exponent,
marked by a letter @Char{p} or @Char{P}. marked by a letter @Char{p} or @Char{P} and written in decimal.
(For instance, @T{0x1.fp10} denotes 1984,
which is @M{0x1f / 16} multiplied by @M{2@sp{10}}.)
A numeric constant with a radix point or an exponent A numeric constant with a radix point or an exponent
denotes a float; denotes a float;
@ -2291,7 +2293,7 @@ the number of parameters in a call to a non-variadic function
@see{func-def}, @see{func-def},
the number of variables in a multiple assignment or the number of variables in a multiple assignment or
a local declaration, a local declaration,
and exactly four for a generic @rw{for} loop. and exactly four values for a generic @rw{for} loop.
The @def{adjustment} follows these rules: The @def{adjustment} follows these rules:
If there are more values than needed, If there are more values than needed,
the extra values are thrown away; the extra values are thrown away;
@ -2310,7 +2312,16 @@ the syntax expects a single expression inside a parenthesized expression;
therefore, adding parentheses around a multires expression therefore, adding parentheses around a multires expression
forces it to produce exactly one result. forces it to produce exactly one result.
Here are some examples. We seldom need to use a vararg expression in a place
where the syntax expects a single expression.
(Usually it is simpler to add a regular parameter before
the variadic part and use that parameter.)
When there is such a need,
we recommend assigning the vararg expression
to a single variable and using that variable
in its place.
Here are some examples of uses of mutlres expressions.
In all cases, when the construction needs In all cases, when the construction needs
@Q{the n-th result} and there is no such result, @Q{the n-th result} and there is no such result,
it uses a @nil. it uses a @nil.
@ -2319,6 +2330,7 @@ print(x, f()) -- prints x and all results from f().
print(x, (f())) -- prints x and the first result from f(). print(x, (f())) -- prints x and the first result from f().
print(f(), x) -- prints the first result from f() and x. print(f(), x) -- prints the first result from f() and x.
print(1 + f()) -- prints 1 added to the first result from f(). print(1 + f()) -- prints 1 added to the first result from f().
local x = ... -- x gets the first vararg argument.
x,y = ... -- x gets the first vararg argument, x,y = ... -- x gets the first vararg argument,
-- y gets the second vararg argument. -- y gets the second vararg argument.
x,y,z = w, f() -- x gets w, y gets the first result from f(), x,y,z = w, f() -- x gets w, y gets the first result from f(),
@ -2331,8 +2343,7 @@ x,y,z = f(), g() -- x gets the first result from f(),
-- z gets the second result from g(). -- z gets the second result from g().
x,y,z = (f()) -- x gets the first result from f(), y and z get nil. x,y,z = (f()) -- x gets the first result from f(), y and z get nil.
return f() -- returns all results from f(). return f() -- returns all results from f().
return ... -- returns all received vararg arguments. return x, ... -- returns x and all received vararg arguments.
return (...) -- returns the first received vararg argument.
return x,y,f() -- returns x, y, and all results from f(). return x,y,f() -- returns x, y, and all results from f().
{f()} -- creates a list with all results from f(). {f()} -- creates a list with all results from f().
{...} -- creates a list with all vararg arguments. {...} -- creates a list with all vararg arguments.