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_archive/rhai_engine/rhaibook/language/assignment-op.md

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+Compound Assignments
+====================
+
+{{#include ../links.md}}
+
+
+Compound assignments are assignments with a [binary operator][operators] attached.
+
+```rust
+number += 8;            // number = number + 8
+
+number -= 7;            // number = number - 7
+
+number *= 6;            // number = number * 6
+
+number /= 5;            // number = number / 5
+
+number %= 4;            // number = number % 4
+
+number **= 3;           // number = number ** 3
+
+number <<= 2;           // number = number << 2
+
+number >>= 1;           // number = number >> 1
+
+number &= 0x00ff;       // number = number & 0x00ff;
+
+number |= 0x00ff;       // number = number | 0x00ff;
+
+number ^= 0x00ff;       // number = number ^ 0x00ff;
+```
+
+
+The Flexible `+=`
+-----------------
+
+The the `+` and `+=` operators are often [overloaded][function overloading] to perform build-up
+operations for different data types.
+
+### Build strings
+
+```rust
+let my_str = "abc";
+
+my_str += "ABC";
+my_str += 12345;
+
+my_str == "abcABC12345"
+```
+
+### Concatenate arrays
+
+```rust
+let my_array = [1, 2, 3];
+
+my_array += [4, 5];
+
+my_array == [1, 2, 3, 4, 5];
+```
+
+### Concatenate BLOB's
+
+```rust
+let my_blob = blob(3, 0x42);
+
+my_blob += blob(5, 0x89);
+
+my_blob.to_string() == "[4242428989898989]";
+```
+
+### Mix two object maps together
+
+```rust
+let my_obj = #{ a:1, b:2 };
+
+my_obj += #{ c:3, d:4, e:5 };
+
+my_obj == #{ a:1, b:2, c:3, d:4, e:5 };
+```
+
+### Add seconds to timestamps
+
+```rust
+let now = timestamp();
+
+now += 42.0;
+
+(now - timestamp()).round() == 42.0;
+```