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fixes #11012

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Araq 2019-04-14 18:28:55 +02:00 • committed by Andreas Rumpf
commit 59ccaa43c7
3 changed files with 28 additions and 50 deletions
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38
lib/pure/strformat.nim
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@ -102,7 +102,9 @@ of ``formatValue`` procs. The required signature for a type ``T`` that supports
formatting is usually ``proc formatValue(result: var string; x: T; specifier: string)``.
The subexpression after the colon
(``arg`` in ``&"{key} is {value:arg} {{z}}"``) is optional. It will be passed as the last argument to ``formatValue``. When the colon with the subexpression it is left out, an empty string will be taken instead.
(``arg`` in ``&"{key} is {value:arg} {{z}}"``) is optional. It will be passed as
the last argument to ``formatValue``. When the colon with the subexpression it is
left out, an empty string will be taken instead.
For strings and numeric types the optional argument is a so-called
"standard format specifier".
@ -215,8 +217,7 @@ Limitations
===========
Because of the well defined order how templates and macros are
expanded, strformat cannot expand template arguments.
expanded, strformat cannot expand template arguments:
.. code-block:: nim
template myTemplate(arg: untyped): untyped =
@ -233,27 +234,6 @@ quoted string literal. It is not an identifier yet. Then the strformat
macro creates the ``arg`` identifier from the string literal. An
identifier that cannot be resolved anymore.
.. code-block:: nim
let x = "abc"
myTemplate(x)
# expansion of myTemplate
let x = "abc"
echo "arg is: ", x
echo &"--- {arg} ---"
# expansion of `&`
let x = "abc"
echo "arg is: ", x
echo:
var temp = newStringOfCap(20)
temp.add "--- "
temp.formatValue arg, "" # arg cannot be resolved anymore
temp.add " ---"
temp
The workaround for this is to bind template argument to a new local variable.
.. code-block:: nim
@ -265,11 +245,12 @@ The workaround for this is to bind template argument to a new local variable.
echo &"--- {arg1} ---"
The use of ``{.inject.}`` here is necessary again because of template
expansion order and hygienic templates. But since we generelly want to
expansion order and hygienic templates. But since we generally want to
keep the hygienicness of ``myTemplate``, and we do not want ``arg1``
to be injected into the context where ``myTemplate`` is expanded,
everything is wrapped in a ``block``.
Future directions
=================
@ -522,8 +503,9 @@ proc formatValue*(result: var string; value: string; specifier: string) =
setLen(value, runeOffset(value, spec.precision))
result.add alignString(value, spec.minimumWidth, spec.align, spec.fill)
template formatValue[T: enum](result: var string; value: T; specifier: string) =
result.add $value
proc formatValue[T](result: var string; value: T; specifier: string) =
mixin `$`
formatValue(result, $value, specifier)
template formatValue(result: var string; value: char; specifier: string) =
result.add value
@ -531,7 +513,7 @@ template formatValue(result: var string; value: char; specifier: string) =
template formatValue(result: var string; value: cstring; specifier: string) =
result.add value
proc formatValue[T](result: var string; value: openarray[T]; specifier: string) =
proc formatValue(result: var string; value: (array|seq|openArray); specifier: string) =
result.add "["
for i, it in value:
if i != 0: