Create Custom Functions\Part 1 - Using Optional Parameters.pq

Author: ninmonkey

Examples-Blog/Custom Functions\Part 1 - Using Optional Parameters.pq

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+let
+    /*
+    About: Compare different optional parameter types
+    This is from the post: https://ninmonkeys.com/blog/2024/06/05/power-query-functions-part1-using-optional-parameters
+
+    lets call Text.Combine() to test declaring optional parameters
+
+
+
+    For this version:
+    - you can pass a null value for a separator
+    - always requires you pass 2 parameters
+    */
+    Join_Nullable = (texts as list, separator as nullable text) =>
+        Text.Combine( texts, separator ),        
+
+    /*
+    For this version:
+    - you can pass a null value for a separator
+    - you can skip the second parameter
+    - 'optional' parameters are automatically 'nullable',
+        so you can drop the 'nullable' part 
+
+    This is how library functions have multiple call signatures
+    Power Query defines one function
+
+    Other languages let you define multiple functions with shared name
+    Based on the argument types, it'll call a different overloaded function
+    */
+    Join_Optional = (texts as list, optional separator as text) =>
+        Text.Combine( texts, separator ),
+        
+    Summary = [
+        chars = { "a".."h" }, // example array of strings
+
+        // this version lets you pass an explicit null value
+        Nullable_1 = Join_Nullable( chars, ", " ),
+        Nullable_2 = Join_Nullable( chars, null ),
+
+        // but it requires you to pass something. It doesn't let you omit a parameter
+        Nullable_3 = Join_Nullable( chars ),
+
+        // this version lets you pass an explicit null value
+        // or drop the parameter completely
+        Join_Optional_1 = Join_Optional( chars, ", " ),
+        Join_Optional_2 = Join_Optional( chars, null ),
+        Join_Optional_3 = Join_Optional( chars )
+    ]
+in Summary