While we all understand that excessive use of ternary operator
may worsen code readability (e.g. nested, multi-line expression),
there are few cases where using it actually improves code
readability. For instance, when a function takes a long list of
arguments out of which one depends on a boolean expression, or
when formatting "yes"/"no" or "on"/"off" values based on a
boolean variable (although one can argue that the latter is a
subset of the former). Just consider alternatives to:

  virBufferAsprintf(buf, "<elem>%s</elem>\n", boolVar ? "yes" : "no");

In fact, this pattern occurs plenty in our code. Exempt it from
our "no ternary operators" rule.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Claudio Fontana <cfontana@suse.de>
---

v2 of:

https://listman.redhat.com/archives/libvir-list/2022-July/233150.html

diff to v1:
- Changed wording, as suggested by Daniel.

 docs/coding-style.rst | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/docs/coding-style.rst b/docs/coding-style.rst
index bf0a80fbc5..81bd4474f1 100644
--- a/docs/coding-style.rst
+++ b/docs/coding-style.rst
@@ -470,7 +470,9 @@ Pointer comparisons may be shortened. All long forms are okay.
     if (!foo)                # or: if (foo == NULL)
 
 New code should avoid the ternary operator as much as possible.
-Specifically it must never span more than one line or nest:
+Its usage in basic cases is warranted (e.g. when deciding between
+two constant strings), however, it must never span more than one
+line or nest.
 
 ::
 
@@ -481,6 +483,9 @@ Specifically it must never span more than one line or nest:
 
     char *foo = bar ? bar->baz ? bar->baz->foo : "nobaz" : "nobar";
 
+  GOOD:
+    virBufferAsprintf(buf, "<element>%s</element>\n", boolVar ? "yes" : "no");
+
 Preprocessor
 ------------
 
-- 
2.35.1

On Mon, Jul 25, 2022 at 05:21:37PM +0200, Michal Privoznik wrote:
> While we all understand that excessive use of ternary operator
> may worsen code readability (e.g. nested, multi-line expression),
> there are few cases where using it actually improves code
> readability. For instance, when a function takes a long list of
> arguments out of which one depends on a boolean expression, or
> when formatting "yes"/"no" or "on"/"off" values based on a
> boolean variable (although one can argue that the latter is a
> subset of the former). Just consider alternatives to:
> 
>   virBufferAsprintf(buf, "<elem>%s</elem>\n", boolVar ? "yes" : "no");
> 
> In fact, this pattern occurs plenty in our code. Exempt it from
> our "no ternary operators" rule.
> 
> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> Reviewed-by: Claudio Fontana <cfontana@suse.de>
> ---
> 
> v2 of:
> 
> https://listman.redhat.com/archives/libvir-list/2022-July/233150.html
> 
> diff to v1:
> - Changed wording, as suggested by Daniel.
> 
>  docs/coding-style.rst | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/coding-style.rst b/docs/coding-style.rst
> index bf0a80fbc5..81bd4474f1 100644
> --- a/docs/coding-style.rst
> +++ b/docs/coding-style.rst
> @@ -470,7 +470,9 @@ Pointer comparisons may be shortened. All long forms are okay.
>      if (!foo)                # or: if (foo == NULL)
>  
>  New code should avoid the ternary operator as much as possible.
> -Specifically it must never span more than one line or nest:
> +Its usage in basic cases is warranted (e.g. when deciding between
> +two constant strings), however, it must never span more than one
> +line or nest.
>  
>  ::
>  
> @@ -481,6 +483,9 @@ Specifically it must never span more than one line or nest:
>  
>      char *foo = bar ? bar->baz ? bar->baz->foo : "nobaz" : "nobar";
>  
> +  GOOD:
> +    virBufferAsprintf(buf, "<element>%s</element>\n", boolVar ? "yes" : "no");
> +
>  Preprocessor
>  ------------

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
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