[jira] [Comment Edited] (JEXL-250) Safe navigation operator

["Dmitri Blinov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JEXL-250?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16353749#comment-16353749 ] 

Dmitri Blinov edited comment on JEXL-250 at 2/6/18 2:29 PM:
------------------------------------------------------------

The following test does not pass for me
{code:java}
    @Test
    public void test250() throws Exception {
        MapContext ctx = new MapContext();
        HashMap<Oject,Object> x = new HashMap<Object, Object> ();
        x.put(2, "123456789");
        ctx.set("x", x);
        JexlEngine engine = new JexlBuilder().strict(true).silent(false).create();
        String stmt = "x.2.class.name";
        JexlScript script = engine.createScript(stmt);
        Object result = script.execute(ctx);
        Assert.assertEquals("java.lang.String", result);

        try {
        stmt = "x.3?.class.name";
        script = engine.createScript(stmt);
        result = script.execute(ctx);
        Assert.assertNull(result);
        } catch(JexlException xany) {
            Assert.fail("Should have evaluated to null");
        }
    }
{code}
The test breaks with {{Should have evaluated to null}}


was (Author: dmitri_blinov):
The following test does not pass for me

{code}
    @Test
    public void test250() throws Exception {
        MapContext ctx = new MapContext();
        HashMap<Object,Object> x = new HashMap<Object, Object> ();
        x.put(2, "123456789");
        ctx.set("x", x);
        JexlEngine engine = new JexlBuilder().strict(true).silent(false).create();
        String stmt = "x.2.class.name";
        JexlScript script = engine.createScript(stmt);
        Object result = script.execute(ctx);
        Assert.assertEquals("java.lang.String", result);

        try {
        stmt = "x?.3.class.name";
        script = engine.createScript(stmt);
        result = script.execute(ctx);
        Assert.assertNull(result);
        } catch(JexlException xany) {
            Assert.fail("Should have evaluated to null");
        }
    }
{code}

The test breaks with {{Should have evaluated to null}}

> Safe navigation operator
> ------------------------
>
>                 Key: JEXL-250
>                 URL: https://issues.apache.org/jira/browse/JEXL-250
>             Project: Commons JEXL
>          Issue Type: New Feature
>    Affects Versions: 3.1
>            Reporter: Dmitri Blinov
>            Assignee: Henri Biestro
>            Priority: Minor
>             Fix For: 3.2
>
>
> It would be more convenient for a script writer to have a kind of safe navigation operator, in the form of, for example, ({{object?.property),}} for null pointer dereferences. I think its quite a common feature of many scripting (and compiled languages) now. The safe operator should work like basic navigation operator for non null values and should short-circuit the entire expression evaluation after encountering null value.
> I see the difference of new operator from the existing lenient mode evaluation in ability to explicitly define places in an expression where {{null}} deference is allowed, for example the expression {code}Order.Customer?.Name{code} defines that each {{Order}} should have a {{Customer}} and only the {{Name}} of the {{Customer}} is optional.
> The difference of new operator from the existing null coalescing {{??}} operator is in its ability to short-circuit evaluation.
> So, safe navigation operator would be a helpful syntaxic sugar which in my opinion does not overlap with an existing functionality.



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