[pkg/ottl] Add StringGetter

.chloggen/ottl-type-specific-getter.yaml

@@ -0,0 +1,16 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: pkg/ottl
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Introduce the concept of type-specific Getters that help simplify type assertions in functions.
+
+# One or more tracking issues related to the change
+issues: [18042]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

pkg/ottl/expression.go

@@ -89,6 +89,33 @@ func (l *listGetter[K]) Get(ctx context.Context, tCtx K) (interface{}, error) {
 	return evaluated, nil
 }
 
+type StringGetter[K any] interface {
+	Get(ctx context.Context, tCtx K) (*string, error)
+}
+
+type IntGetter[K any] interface {
+	Get(ctx context.Context, tCtx K) (*int64, error)
+}
+
+type StandardTypeGetter[K any, T any] struct {
+	Getter func(ctx context.Context, tCx K) (interface{}, error)
+}
+
+func (g StandardTypeGetter[K, T]) Get(ctx context.Context, tCtx K) (*T, error) {
+	val, err := g.Getter(ctx, tCtx)
+	if err != nil {
+		return nil, err
+	}
+	if val == nil {
+		return nil, nil
+	}
+	v, ok := val.(T)
+	if !ok {
+		return nil, fmt.Errorf("expected %T but got %T", v, val)
+	}
+	return &v, nil
+}
+
 func (p *Parser[K]) newGetter(val value) (Getter[K], error) {
 	if val.IsNil != nil && *val.IsNil {
 		return &literal[K]{value: nil}, nil

pkg/ottl/expression_test.go

@@ -318,3 +318,46 @@ func Test_newGetter(t *testing.T) {
 		assert.Error(t, err)
 	})
 }
+
+func Test_StandardTypeGetter(t *testing.T) {
+	tests := []struct {
+		name             string
+		getter           StandardTypeGetter[interface{}, string]
+		want             interface{}
+		valid            bool
+		expectedErrorMsg string
+	}{
+		{
+			name: "Correct type",
+			getter: StandardTypeGetter[interface{}, string]{
+				Getter: func(ctx context.Context, tCx interface{}) (interface{}, error) {
+					return "str", nil
+				},
+			},
+			want:  "str",
+			valid: true,
+		},
+		{
+			name: "Incorrect type",
+			getter: StandardTypeGetter[interface{}, string]{
+				Getter: func(ctx context.Context, tCx interface{}) (interface{}, error) {
+					return true, nil
+				},
+			},
+			valid:            false,
+			expectedErrorMsg: "expected string but got bool",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			val, err := tt.getter.Get(context.Background(), nil)
+			if tt.valid {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, *val)
+			} else {
+				assert.EqualError(t, err, tt.expectedErrorMsg)
+			}
+		})
+	}
+}

pkg/ottl/functions.go

@@ -151,6 +151,18 @@ func (p *Parser[K]) buildArg(argVal value, argType reflect.Type) (any, error) {
 			return nil, err
 		}
 		return arg, nil
+	case strings.HasPrefix(name, "StringGetter"):
+		arg, err := p.newGetter(argVal)
+		if err != nil {
+			return nil, err
+		}
+		return StandardTypeGetter[K, string]{Getter: arg.Get}, nil
+	case strings.HasPrefix(name, "IntGetter"):
+		arg, err := p.newGetter(argVal)
+		if err != nil {
+			return nil, err
+		}
+		return StandardTypeGetter[K, int64]{Getter: arg.Get}, nil
 	case name == "Enum":
 		arg, err := p.enumParser(argVal.Enum)
 		if err != nil {

pkg/ottl/functions_test.go

@@ -462,7 +462,7 @@ func Test_NewFunctionCall(t *testing.T) {
 								{
 									Literal: &mathExprLiteral{
 										Converter: &converter{
-											Function: "Testing_getter",
+											Function: "testing_getter",
 											Arguments: []value{
 												{
 													Literal: &mathExprLiteral{
@@ -599,7 +599,7 @@ func Test_NewFunctionCall(t *testing.T) {
 								{
 									Literal: &mathExprLiteral{
 										Converter: &converter{
-											Function: "Testing_getter",
+											Function: "testing_getter",
 											Arguments: []value{
 												{
 													Literal: &mathExprLiteral{
@@ -623,6 +623,32 @@ func Test_NewFunctionCall(t *testing.T) {
 			},
 			want: nil,
 		},
+		{
+			name: "stringgetter arg",
+			inv: invocation{
+				Function: "testing_stringgetter",
+				Arguments: []value{
+					{
+						String: ottltest.Strp("test"),
+					},
+				},
+			},
+			want: nil,
+		},
+		{
+			name: "intgetter arg",
+			inv: invocation{
+				Function: "testing_intgetter",
+				Arguments: []value{
+					{
+						Literal: &mathExprLiteral{
+							Int: ottltest.Intp(1),
+						},
+					},
+				},
+			},
+			want: nil,
+		},
 		{
 			name: "string arg",
 			inv: invocation{
@@ -872,6 +898,18 @@ func functionWithGetter(Getter[interface{}]) (ExprFunc[interface{}], error) {
 	}, nil
 }
 
+func functionWithStringGetter(StringGetter[interface{}]) (ExprFunc[interface{}], error) {
+	return func(context.Context, interface{}) (interface{}, error) {
+		return "anything", nil
+	}, nil
+}
+
+func functionWithIntGetter(IntGetter[interface{}]) (ExprFunc[interface{}], error) {
+	return func(context.Context, interface{}) (interface{}, error) {
+		return "anything", nil
+	}, nil
+}
+
 func functionWithString(string) (ExprFunc[interface{}], error) {
 	return func(context.Context, interface{}) (interface{}, error) {
 		return "anything", nil
@@ -943,7 +981,8 @@ func defaultFunctionsForTests() map[string]interface{} {
 	functions["testing_setter"] = functionWithSetter
 	functions["testing_getsetter"] = functionWithGetSetter
 	functions["testing_getter"] = functionWithGetter
-	functions["Testing_getter"] = functionWithGetter
+	functions["testing_stringgetter"] = functionWithStringGetter
+	functions["testing_intgetter"] = functionWithIntGetter
 	functions["testing_string"] = functionWithString
 	functions["testing_float"] = functionWithFloat
 	functions["testing_int"] = functionWithInt