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Manual a little more clear about string->number coersions

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Roberto Ierusalimschy 2019-12-05 12:57:40 -03:00
parent 81f2401c6d
commit e174f43807
1 changed files with 25 additions and 16 deletions
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@ -1406,10 +1406,9 @@ It has the following syntax:
exp @bnfter{,} exp @bnfopt{@bnfter{,} exp} @Rw{do} block @Rw{end}} exp @bnfter{,} exp @bnfopt{@bnfter{,} exp} @Rw{do} block @Rw{end}}
} }
The given identifier (@bnfNter{Name}) defines the control variable, The given identifier (@bnfNter{Name}) defines the control variable,
which is local to the loop body (@emph{block}). which is a new variable local to the loop body (@emph{block}).
The loop starts by evaluating once the three control expressions; The loop starts by evaluating once the three control expressions.
they must all result in numbers.
Their values are called respectively Their values are called respectively
the @emph{initial value}, the @emph{limit}, and the @emph{step}. the @emph{initial value}, the @emph{limit}, and the @emph{step}.
If the step is absent, it defaults @N{to 1}. If the step is absent, it defaults @N{to 1}.
@ -1417,8 +1416,9 @@ If the step is absent, it defaults @N{to 1}.
If both the initial value and the step are integers, If both the initial value and the step are integers,
the loop is done with integers; the loop is done with integers;
note that the limit may not be an integer. note that the limit may not be an integer.
Otherwise, the loop is done with floats. Otherwise, the three values are converted to
(Beware of floating-point accuracy in this case.) floats and the loop is done with floats.
Beware of floating-point accuracy in this case.
After that initialization, After that initialization,
the loop body is repeated with the value of the control variable the loop body is repeated with the value of the control variable
@ -1773,9 +1773,24 @@ If it does, that representation is the result.
Otherwise, the conversion fails. Otherwise, the conversion fails.
Several places in Lua coerce strings to numbers when necessary. Several places in Lua coerce strings to numbers when necessary.
In particular,
the string library sets metamethods that try to coerce
strings to numbers in all arithmetic operations.
If the conversion fails,
the library calls the metamethod of the other operand
(if present) or it raises an error.
Note that bitwise operators do not do this coercion.
Nonetheless, it is always a good practice not to rely on these
implicit coercions, as they are not always applied;
in particular, @T{"1"==1} is false and @T{"1"<1} raises an error
@see{rel-ops}.
These coercions exist mainly for compatibility and may be removed
in future versions of the language.
A string is converted to an integer or a float A string is converted to an integer or a float
following its syntax and the rules of the Lua lexer. following its syntax and the rules of the Lua lexer.
(The string may have also leading and trailing whitespaces and a sign.) The string may have also leading and trailing whitespaces and a sign.
All conversions from strings to numbers All conversions from strings to numbers
accept both a dot and the current locale mark accept both a dot and the current locale mark
as the radix character. as the radix character.
@ -1783,15 +1798,9 @@ as the radix character.
If the string is not a valid numeral, If the string is not a valid numeral,
the conversion fails. the conversion fails.
If necessary, the result of this first step is then converted If necessary, the result of this first step is then converted
to the required number subtype following the previous rules to a specific number subtype following the previous rules
for conversions between floats and integers. for conversions between floats and integers.
The string library uses metamethods that try to coerce
strings to numbers in all arithmetic operations.
If the conversion fails,
the library calls the metamethod of the other operand
(if present) or it raises an error.
The conversion from numbers to strings uses a The conversion from numbers to strings uses a
non-specified human-readable format. non-specified human-readable format.
To convert numbers to strings in any specific way, To convert numbers to strings in any specific way,
@ -7687,8 +7696,8 @@ This library provides basic mathematical functions.
It provides all its functions and constants inside the table @defid{math}. It provides all its functions and constants inside the table @defid{math}.
Functions with the annotation @St{integer/float} give Functions with the annotation @St{integer/float} give
integer results for integer arguments integer results for integer arguments
and float results for float (or mixed) arguments. and float results for non-integer arguments.
the rounding functions The rounding functions
@Lid{math.ceil}, @Lid{math.floor}, and @Lid{math.modf} @Lid{math.ceil}, @Lid{math.floor}, and @Lid{math.modf}
return an integer when the result fits in the range of an integer, return an integer when the result fits in the range of an integer,
or a float otherwise. or a float otherwise.
@ -7843,7 +7852,7 @@ The results from this function have good statistical qualities,
but they are not cryptographically secure. but they are not cryptographically secure.
(For instance, there are no guarantees that it is hard (For instance, there are no guarantees that it is hard
to predict future results based on the observation of to predict future results based on the observation of
some number of previous results.) some previous results.)
} }