How to get memory usage of my application and system in swift by programatically

For Swift 3.0 you can use the following function.

func report_memory() {
    var taskInfo = mach_task_basic_info()
    var count = mach_msg_type_number_t(MemoryLayout<mach_task_basic_info>.size)/4
    let kerr: kern_return_t = withUnsafeMutablePointer(to: &taskInfo) {
        $0.withMemoryRebound(to: integer_t.self, capacity: 1) {
            task_info(mach_task_self_, task_flavor_t(MACH_TASK_BASIC_INFO), $0, &count)
        }
    }

    if kerr == KERN_SUCCESS {
        print("Memory used in bytes: \(taskInfo.resident_size)")
    }
    else {
        print("Error with task_info(): " +
            (String(cString: mach_error_string(kerr), encoding: String.Encoding.ascii) ?? "unknown error"))
    }
}

mAc's answers but without force unwrapping:

func memoryFootprint() -> String {
    // The `TASK_VM_INFO_COUNT` and `TASK_VM_INFO_REV1_COUNT` macros are too
    // complex for the Swift C importer, so we have to define them ourselves.
    let TASK_VM_INFO_COUNT = mach_msg_type_number_t(MemoryLayout<task_vm_info_data_t>.size / MemoryLayout<integer_t>.size)
    guard let offset = MemoryLayout.offset(of: \task_vm_info_data_t.min_address) else {return "memory: NA"}
    let TASK_VM_INFO_REV1_COUNT = mach_msg_type_number_t(offset / MemoryLayout<integer_t>.size)
    var info = task_vm_info_data_t()
    var count = TASK_VM_INFO_COUNT
    let kr = withUnsafeMutablePointer(to: &info) { infoPtr in
        infoPtr.withMemoryRebound(to: integer_t.self, capacity: Int(count)) { intPtr in
            task_info(mach_task_self_, task_flavor_t(TASK_VM_INFO), intPtr, &count)
        }
    }
    guard
        kr == KERN_SUCCESS,
        count >= TASK_VM_INFO_REV1_COUNT
    else { return "memory: NA" }
    
    let usedBytes = Float(info.phys_footprint)
    let usedBytesInt: UInt64 = UInt64(usedBytes)
    let usedMB = usedBytesInt / 1024 / 1024
    let usedMBAsString: String = "memory: \(usedMB) MB"
    return usedMBAsString
}

Found and tested this on XCode 12.2 and Mac OS Catalina 10.15.6 and it works like charm:

func memoryFootprint() -> Float? {
    // The `TASK_VM_INFO_COUNT` and `TASK_VM_INFO_REV1_COUNT` macros are too
    // complex for the Swift C importer, so we have to define them ourselves.
    let TASK_VM_INFO_COUNT = mach_msg_type_number_t(MemoryLayout<task_vm_info_data_t>.size / MemoryLayout<integer_t>.size)
    let TASK_VM_INFO_REV1_COUNT = mach_msg_type_number_t(MemoryLayout.offset(of: \task_vm_info_data_t.min_address)! / MemoryLayout<integer_t>.size)
    var info = task_vm_info_data_t()
    var count = TASK_VM_INFO_COUNT
    let kr = withUnsafeMutablePointer(to: &info) { infoPtr in
        infoPtr.withMemoryRebound(to: integer_t.self, capacity: Int(count)) { intPtr in
            task_info(mach_task_self_, task_flavor_t(TASK_VM_INFO), intPtr, &count)
        }
    }
    guard
        kr == KERN_SUCCESS,
        count >= TASK_VM_INFO_REV1_COUNT
    else { return nil }
    
    let usedBytes = Float(info.phys_footprint)
    return usedBytes
    
}

func formattedMemoryFootprint() -> String {
    let usedBytes: UInt64? = UInt64(self.memoryFootprint() ?? 0)
    let usedMB = Double(usedBytes ?? 0) / 1024 / 1024
    let usedMBAsString: String = "Memory Used by App: \(usedMB)MB"
    return usedMBAsString
}

Hope this helps someone too :)