Concat(s0, s1, ..sN)

README.md

@@ -184,7 +184,8 @@ calling a function will be undefined if:
 
 | Function | Description |
 | :--- | :--- |
-| `Coalesce(p0, p1, ..pN)` | Returns the first defined, non-null argument. |
+| `Coalesce(p0, p1, [..pN])` | Returns the first defined, non-null argument. |
+| `Concat(s0, s1, [..sN])` | Concatenate two or more strings. |
 | `Contains(s, t)` | Tests whether the string `s` contains the substring `t`. |
 | `ElementAt(x, i)` | Retrieves a property of `x` by name `i`, or array element of `x` by numeric index `i`. |
 | `EndsWith(s, t)` | Tests whether the string `s` ends with substring `t`. |

src/Serilog.Expressions/Expressions/Compilation/Variadics/VariadicCallRewriter.cs

@@ -18,7 +18,7 @@
 
 namespace Serilog.Expressions.Compilation.Variadics
 {
-    // Now a bit of a misnomer - handles variadic `coalesce()`, as well as optional arguments for other functions.
+    // Handles variadic `coalesce()` and `concat()`, as well as optional arguments for other functions.
     class VariadicCallRewriter : IdentityTransformer
     {
         static readonly VariadicCallRewriter Instance = new VariadicCallRewriter();
@@ -39,7 +39,8 @@ protected override Expression Transform(CallExpression call)
                 return new CallExpression(call.IgnoreCase, call.OperatorName, operands);
             }
 
-            if (Operators.SameOperator(call.OperatorName, Operators.OpCoalesce))
+            if (Operators.SameOperator(call.OperatorName, Operators.OpCoalesce) ||
+                Operators.SameOperator(call.OperatorName, Operators.OpConcat))
             {
                 if (call.Operands.Length == 0)
                     return CallUndefined();
@@ -64,7 +65,7 @@ protected override Expression Transform(CallExpression call)
 
         static CallExpression CallUndefined()
         {
-            return new CallExpression(false, Operators.OpUndefined);
+            return new(false, Operators.OpUndefined);
         }
     }
 }

src/Serilog.Expressions/Expressions/Operators.cs

@@ -29,6 +29,7 @@ static class Operators
         // RuntimeOp* means runtime only.
 
         public const string OpCoalesce = "Coalesce";
+        public const string OpConcat = "Concat";
         public const string OpContains = "Contains";
         public const string OpElementAt = "ElementAt";
         public const string OpEndsWith = "EndsWith";

src/Serilog.Expressions/Expressions/Runtime/RuntimeOperators.cs

@@ -461,6 +461,16 @@ public static LogEventPropertyValue _Internal_IsNotNull(LogEventPropertyValue? v
             return new ScalarValue(str.Substring((int)si, (int)len));
         }
 
+        public static LogEventPropertyValue? Concat(LogEventPropertyValue? first, LogEventPropertyValue? second)
+        {
+            if (Coerce.String(first, out var f) && Coerce.String(second, out var s))
+            {
+                return new ScalarValue(f + s);
+            }
+
+            return null;
+        }
+
         // ReSharper disable once ReturnTypeCanBeNotNullable
         public static LogEventPropertyValue? IndexOfMatch(StringComparison sc, LogEventPropertyValue? corpus, LogEventPropertyValue? regex)
         {

test/Serilog.Expressions.Tests/Cases/expression-evaluation-cases.asv

@@ -208,6 +208,10 @@ ismatch('foo', '^o')                 ⇶ false
 indexofmatch('foo', 'x')             ⇶ -1
 substring('abcd', 1, 2)              ⇶ 'bc'
 substring('abcd', 1)                 ⇶ 'bcd'
+concat('a', 'b', 'c')                ⇶ 'abc'
+concat('a', 42, 'c')                 ⇶ undefined()
+concat('a', undefined())             ⇶ undefined()
+concat(undefined(), 'b')             ⇶ undefined()
 
 // Conditional
 if true then 1 else 2                ⇶ 1